Gas Furnace Training Class! Basics, Operation, Components, Troubleshooting

in this hvacr training video i'm going over all the different types of gas furnace components that you can run into when you're servicing gas furnaces out in the field from 60 efficient furnaces all the way up to say 98 efficient gas furnaces we're going to be going over that coming up [Music] so the object of today is to determine where your pain points are for when you're servicing a gas furnace so we need to know what all the internal components are that you can run into in the field we're going to be going over some of the history of gas furnaces in each of the components and how you troubleshoot them what you really need to think about is we have a kind of a evolution of gas furnaces over the last 60 80 years and you can have just a variety of different components inside this first example is just kind of the operation of an 80 efficient gas furnace just to get started this would be a furnace that you would install inside of a building those are ones that you'd have outside those are called gas furnace package units on a call for heat you have to have your your door switch closed and you're going to have that call on w on the control board on a normal 80 efficient gas furnace here's a wiring diagram for a gas furnace and air conditioning system and you see that we're running 18 6 thermostat wire and we have our thermostat we have our gas furnace and then we have our outdoor condensing unit white is w and that is for heat we have y that's yellow and that's for air conditioning we have r that's red and that's power 24 volts and we have g that is green and that's for the fan and we have c and c is your common or your path back in order to power your thermostat what you are doing inside the thermostat is you are connecting r and w so once you have 24 volts on the furnace control board because you remember you have 24 volts on the r on the furnace control board and you can measure that with a multimeter between r and c once you measure on a gas furnace between w and c and you measure 24 volts anywhere from say 24 to 29 and a half volt with the door switch shot that means that you do have a call for heat for that furnace here we have our basic sequence of operation for an 80 efficient gas furnace so when we have a call for heat on a gas furnace then we have our inducer motor turns on first our pressure switch electrically closes proving that the inducer motor is running and then we have our hot surface igniter is powered and heats up and it turns cherry red and then we have our gas valve is powered with 24 volts remember it's like 24 to 29 and a half volts and then it mechanically opens allowing gas to go through then we have our flame proving process which is our control board and our flame sensor it's really not a flame sensor it's just a flame rod and we are proving the flame on the ground for the furnace and there's a dedicated ground on that control board then we have a blower on delay which is starting at the control board it's like a timing mechanism allowing the heat exchanger to heat up before turning the blower motor on which is step seven is when our control board powers the blower motor to push the worm air through the building now we're going to expand on all these components as we move through this this is just the general sequence of operation for a standard 80 efficient furnace you are arriving at the site you're listening to the customer and you're you're already starting to think what could be the problem as you're walking up to the gas furnace you're going to see the efficiency kind of as you're walking up to it so a 60 efficient furnace that's going to have a cold air intake and that is a rectangle opening and what it's doing is after you have your your heat rising from your burner tray which is down low in the 60 or 70 efficient furnace it's going to rise naturally up through the heat exchanger and then it's going to get mixed with the cold air before going up into the exhaust to lower the stack effect so you're lowering the speed in which the exhaust is going up through the exhaust pipe and so basically you're trying to lengthen the time in which the exhaust is is traveling through the heat exchanger as the air is blowing by it which is the conditioned air in the house we're in a building then we have our 80 efficient gas furnace and you're going to notice louvers on it on 80 efficient furnace so it's not going to have a large rectangle cold air intake just going to have louvers and you're going to also see a metal exhaust so a lot of times you're going to see a bee vent exhaust which is a double wall exhaust pipe but the whole point is you're going to have metal on a 60 or 70 percent efficient furnace you're going to have metal exhaust on 80 efficient furnace and then when you get over to a 90 efficient furnace you're going to have pvc exhaust and you may have a second pipe and that's for the combustion air 90 efficient gas furnace is able to draw so much heat out of the exhaust that the temperature of the exhaust is almost basically the temperature of your skin and so it can travel from the furnace to the exterior of the building through just pvc instead of metal exhaust pipe because the temperature of the exhaust is low the other thing is it's pvc because you're going to have water condensing and water is created during the flame process on a 90 efficient gas furnace and so any uh basically any humidity that's going to condense in the exhaust pipe so you want it trickling back into the furnace and then it's going to drain out the drain on the furnace and so you're going to also see a pvc drain as well so that's several indicators for you to know it's a 90 efficient furnace there is no louvers on it usually so you're going to have either one or two pvc uh pipes right here one's gonna be the exhaust one's gonna be the intake on a 80 efficient furnace you have to think hey how high of an efficiency can a gas furnace that's outside big if you're going to condense some of the water created during the flame process due to that chemical reaction and you're trying to basically just vent that out of a out of a trap what's going to happen is outside it's going to freeze a standard package unit's only going to be say 80 or 83 percent efficient changing the gas into heat energy and then the rest of the heat is going to have to go outside right out of the exhaust pipe along with that humidity now we're going to get into some of the history of the gas furnaces and some of the components inside and so you just want to be aware of all this stuff so when you're walking up to a service call you know what you're looking at you have back back when and we have some of these still installed in some of the vacation homes down down by the bay where where i live at so we have our ocean on one side bay on the other side so it was a resort town they just stuck these gas furnaces right into the floor and this is just a natural natural giraffe convection uh floor furnace and so you'll have this in the hallway in some of these homes and so the heater is just hanging in the crawl space inside of this you don't have you don't have a 120 volt power supply powering this furnace you just have a 750 millivolt gas valve and so you have a 750 millivolt thermopile and then you have a thermostat that is low electrical resistance when it's making the contacts and so the whole point is that it's not going to lower the voltage across the contact uh in order to turn the turn the heat on and power the gas valve it's very important that you get a thermostat that's made for a 750 millivolt system right here you can see here's a close-up image and you have the wiring right there on the thtp that's kind of the common for that gas valve and then tp so tp is for the the thermopile uh for it to basically open up the the solenoid or hold it open and then you have your th to thtp that is basically what's getting broken by your thermostat and on a call for heat you're connecting the circuit and allowing power to that stage inside of the inside of the gas valve and so you're allowing the the gas flow to come out when you are powering it with your 750 millivolt gas valve so you just got to remember one is to hold the the pilot open and then the second is to open the main gas and so what you need to think about with some of these are that when you have a load on the main gas you should not be dropping any lower than say 190 millivolts and if you did that would indicate maybe that you don't have a flame kind of enveloping the thermopile or maybe it's out of position or maybe the thermopile is bad you really want to shoot for something closer to say 250 millivolts when you are powering your main gas so you got to have it high enough in order to electrically or mechanically open that solenoid valve anyway so we have 60 efficient gas furnaces we're not going to spend a whole lot of time but i just want to kind of give you some of the components that are in these systems because you may find some of these same components even in 80 efficient furnaces but once again you see a cold air intake right there in the front of this furnace some of the oldest furnaces do not have control boards but they have a fan center control so it's very important for you to know what that is we have our general purpose relay right here and you have a transformer and then you have your plug and wiring you can see that right here so fan center control is made up of a 24 volt transformer a thermostat terminal plate and it's not all connected it's only the common and the hot and then you have a plug and a general purpose relay so we have videos on general purpose relays we have a video on the fan center control so if your pain point is not knowing what that is or either one of those components make sure that you are watching a video on that in order to determine what that is so that when you see it you're not overwhelmed a lot of technicians end up getting overwhelmed because there's just a big jumble of wires and several components that they're not aware of or they're not confident in troubleshooting or don't know how they work but if you know how each of the components work when you open up the furnace you're it's going to be very much easier in order for you to diagnose what the problem is once you have confidence and you understand each of the components fan limit switches so this is not only a limit in order to stop the furnace from over firing or say overheating but it's also a mechanism to turn the blower motor on and off during heating mode right here on the dial you're going to see three little pieces right here this this top piece right here you see it's set at about 165 or so that is the limit okay so that is going to shut off the the power to the gas valve we have right here the second one the one in the middle is at about 125 or so 120 that 120 degrees fahrenheit by the way that is when the furnace blower motor is going to turn on and then we have our last uh piece right here on the dial and that is set at about 90 degrees and so you want to think about uh this dial being set at the proper um proper amount because this is when the blur motor turns off if you set this down at say 70 degrees and it's 74 in the building it's never going to turn off it's never going to turn the blower motor off and so you want to know that it's going to shut off properly as well this this bi-metal right here tends to get out of parameters due to contraction and expansion over its lifetime and so if you have it set down too low say you're trying to eke out that last amount of efficiency out of a warm heat exchanger and you set it down to 80 80 degrees once it gets out of parameter it may be 72 degrees and it's still not turning the blower motor off you want to think about that as a service tech as well if you just push this up a little bit you're probably going to notice that the blower motor is going to shut off it's also important for you to know what temperature it is in the heat exchanger while you're setting this stuff like if you're troubleshooting and you think it's overheating or something like that you want a good temperature meter in order to take your measurements so i just want you to know how this how this works we have another a video on the faint limit switches they also have a button in order to bypass so you could uh push that in or pull it out so pulling it out leaves on auto pushing it in is going to turn the blur motor and keep it on all the time so we have furnaces that use a shaded pole blower motor or we use we have ones that use a capacitor the ones that don't have a capacitor on the outside and it does have holes in the frame and it's on an older furnace those are shaded pole blower motors there is no capacitor that are less electrically efficient than a permanent split capacitor blower motor one that needs a capacitor to start and to run on some of the older gas furnaces you're going to see a burner tray just like say on a cast iron boiler you'll see a burner tray instead of burner tubes and so you just have this entire tray with your flame and then you just have your exhaust rising naturally you have a manually lit system so this is a combination gas valve but you have a 30 millivolt thermocouple and that's attached to a solenoid and that solenoid may need about say 13 millivolts in order to hold the solenoid in place so just because you have power at the the thermocouple does not mean that the solenoid is going to suck in on these combination gas valves and also on the 750 millivolt gas valves you have to first do the work of pushing the solenoid in by pressing in on the button and then the the thermocouple has to heat up same thing with the thermopile has to heat up in order to create the millivolts the power in order to hold the solenoid in place so every solenoid is different but i would say the minimum that you're going to you're going to want to measure with a load would be 13 millivolts but of course you would like to have higher maybe 20 25 or close to 30 that would be great and then you can just power this with 24 volts for the main gas flow to come through but once again your your thermocouple is the flame proving process and it's holding that first valve area open in order for you to when you power it with 24 volts it'll allow the the gas flow to go to go through so once again it's a combination gas valve so the next step in the kind of the evolution of gas furnaces and when i say evolution i don't mean carrier brian i just mean things have changed over a long period of time is the intermittent pilot gas valve so with this type of a gas valve you don't have any thermocouple you don't have a thermal pile or anything like that and so what you have is you have your you're powering your pilot valve and that's going to allow gas to come through your pilot over to the pilot head and then when you power your main gas valve it's going to allow the full gas through when i say full gas through what i really mean is say natural gas runs at say five to eight inch water column it's actually going to allow say around 3.5 inch water column going through but we'll get to that in a little bit along with these intermittent pilot gas valves we also have our intermittent pilot ignition modules these were the first control boards kind of in gas furnaces and so you're still going to see these in 90 efficient gas furnaces you're going to see them in boilers and pool heaters and all kinds of all kinds of stuff these were typically spark ignition at least the first ones were we have the intermittent pilot control modules matched with the intermittent pilot gas valve and so these modules use flame rectification in order to prove the flame here you see that we have our two rod set up so one rod is the flame sensor and the rod that you see is very close to the termination head which is right here this is the termination head and here is the the spark rod it's about one eighth of an inch right there and that's about what's needed in order for the say ten thousand volts so anywhere from say six thousand to twenty thousand volts to jump across there but typically it's around ten thousand to spark and then you have your gas coming out of the pilot head and it's being ignited as you can see right here your flame rod is kind of out of the way the flame so this will be bad if that's spun and it was out of the way of the flame because the flame may be a little closer to the pilot head over on this one over here you can see that the flame rod is closer to the pilot head and so that rod is going to get enveloped in the flame and the flame is going to complete the electrical circuit that's what's important to know about this is the flame right there is going to prove that the flame exists by completing the electrical circuit it's also going to be rectifying alternating current and changing it to direct current and that direct current is going to be seen on the ignition module over here we're going to get into flame notification in a bit but the whole point of this is that on these ignition modules uh with these uh the intermittent pilot ignition modules you're going to check for flame notification on the ground it's important to check it on the ground because some of these uh don't have a two rod set up some of them are a single rod setup and what that means is that the sparker and flame rod are one in the scene and so it can be a little confusing so we would just check it from the gnd flame notification with our multimeter in series between the g and d and the wire that attaches to the ground frame of the gas valve or you know we can just go ahead and clip it to this ground so what's happening is on the the pilot head it's using the pilot tube as a ground wire going back to the gas valve and then we have a wire going from the gas valve going over to the gnd on the intermittent uh pilot module control module if you were to disconnect the gnd wire off of that module the flame is going to shut off because that's how the flame rectification signal is getting back to that board moving on from say 60 efficient gas furnaces to eighty percent efficient uh we have louvers on the furnace right here so you can see that you can see a metal exhaust pipe so same right there louvers and a metal exhaust pipe what you have now is an inducer motor so the inducer motor is pulling the exhaust through the longer heat exchanger and you're attaining a higher efficiency in changing the gas from well from gas to heat energy but you're not losing as much out of the exhaust pipe you can also have a furnace be multi-poised because you're pulling the exhaust through it it's no longer has to be gravity now examples of 80 efficient gas furnace heat exchangers you can see that they're very long so they can be made several different ways and then you have the gas furnaces are using on these 80 efficient furnaces they're using burner tubes instead of burner trays so the whole point is that it's mixing the the the gas in the air right here just like on the burner tray but then what's happening is you have the flame sitting on the front of the burner retention head over here then the exhaust enters into the heat exchanger once it enters into the heat exchanger it gets pulled through that whole thing and then pulled through the inducer motor and then pushed out through the exhaust pipe so 80 efficient furnaces have an inducer motor that's either a shaded pole inducer motor or it's a pse inducer motor so shaded pull means there is no capacitor on the side of that inducer motor so you won't see that and it'll look just like a say a fan motor or say on a microwave or maybe a walk-in box or something like that there is no capacitor now sometimes you have to be careful because there's a little box on the side of the inducer motor that may house a square type of capacitor instead of a metal larger type capacitor the whole point is that when that capacitor fails you want to or even before that obviously you want to go ahead and replace that with the same mfd rating so the microfarad rating but the same or higher voltage rating that means that if you don't have one of these little black ones you can replace a small black capacitor with a larger one as long as it's the same microfarad reading but the same or higher voltage rating now older inducer motors may have oil ports and so you'll see maybe one here and then one up towards the front and you want to make sure to oil that say uh two times a season uh one at the beginning heating season one towards the middle or end and the whole point is that you want to fill up that that felt pad so it holds all the oil and then it gets drawn into the oil bearing an oil bearing is nothing more than one piece of of metal that's in a fixed position and another one that's rotating on the inside of it and you have a film of oil in between the two if that dries out the metal is going to rub on the other piece of metal it's going to cause friction it could even potentially cause a fire on that inducer motor but a lot of times what we see as technicians in the field is that that inducer motor is seized up so if you go and oil it after it's seized up it's almost a almost a guarantee that it's going to be seizing up again and so you got to think you're going to be replacing that inducer motor you don't want to just oil it and say hey i fixed it and that's it you're going to want to replace that inducer motor with a a wheel like a oil sealed bearing inducer motor so one that does not have oil ports on it all 80 efficient furnaces have an inducer motor with a metal shroud around it so it's not plastic on the 80 efficient furnace because the exhaust temperature is still high well the problem with this whole thing is that the inducer motor wheel a lot of times is going to rot due to the water vapor in the exhaust it's just going to rot and you might lose blades you might lose the entire fan blade assembly with these tend to fail faster or sooner than a 90 efficient furnace would that in a 90 efficient furnace inducer motor would be plastic so next we have our pressure switch and the pressure switch is one of the most maybe misunderstood items in a gas furnace and a lot of times there's tubes going all over the place you may have one pressure switch you may have three or even four pressure switches inside of a gas furnace and you need to know what's going on first of all you need to know how that pressure switch works and so we have a video on on how pressure switches work and so make sure to check that out the pressure switch proves that the inducer motor is functioning the exhaust is not clogged and it has multiple other functions uh depending on where the pressure switch is mounted as far as the condensate drain and things like that condensate trap on a pressure switch you're gonna have a tag in this case it says 0.8 inch water column so what you need to really think about is one psi equals 27.6 inches of water column and so what we're really talking about is a very very small change from atmospheric pressure you're looking for a pressure differential needed in order to close the electrical switch of a pressure switch right here you see there's an air chamber a spring a diaphragm and then you have your switching mechanism and then you have your other side your other air chamber pressure switches may or may not have the watercolumn rating on the tag you may have to look up the model number in google uh or in in a in a trade part program in order to determine you know what the rating actually is for that pressure switch in order to test it here we have the inside of a pressure switch you can see it's closing so normally it's going to be like this it's going to be electrically open if there is two tabs one here and one here but some have three that means that one switch is normally closed and one is normally open and when the pressure lowers on the spring side so it's the you have two air chambers and so when the pressure lowers on the on the spring side and this pressure is not necessarily increased it's just you have a differential of pressure it's going to overcome the spring pressure it's going to close the normally open set of contacts and it's going to open up the normally closed set of contacts here we're just going to take a look at our two air chambers each chamber has a hole in it and so that's very important to know so even if you don't have a port like that you can see that you're going to connect a hose to on the one side there is still a tiny little hole there and then you have where you're going to connect your hose to on the other side and that's always on the the side that has the spring and remember that the spring is adjustable and so you if you were to look on the back of a pressure switch you're going to see like some glue there and so if you were to take that glue off you could actually adjust that but you don't want to adjust a like a pressure switch that's inspect for that particular furnace but you can install your adjustable pressure switch and set it to the proper inches of water column measurement that the furnace is looking for for that inducer motor and uh and condensate trap testing the pressure switch while it's connected to the system you can disconnect the two wires that are going to the pressure switch so one should be 24 volt hot and the other one will will just not have any power on it it's basically once those two are connected it's proving that the inducer motor is running so if you were to disconnect those and just put them somewhere where they're not going to um arc against the the ground frame and then what you're going to do is turn the heat on and you're going to t in between the pressure switch and the inducer motor if if you're talking about a single port pressure switch it's also important to note that that pressure switch has to be vertical it still has to be like like this right here it cannot be flat like that because then you're adding more pressure down onto that spring you're adding the entire diaphragm weight down onto that spring so it has to be like this and then you can go ahead and check your water column measurement this particular tool right here this is the field piece sdmn6 that one right there comes with some wires and an indicator light telling you if the switch is closed or open i don't like to do that i like to have a multimeter connected onto that pressure switch so that i can read the electrical resistance when it is open the switch is open i should be reading ol on my multimeter when i'm reading electrical resistance when it's closed i should be reading 0.0 ohms of electrical resistance meaning there's no electrical resistance a stopping electrical flow once i add power to one of those terminals in order for it to come across come across a switch if that pressure switch was measuring say one or two ohms or three ohms of electrical resistance that means that the contacts are pitted and bad and that could be the problem i want to see that i want to see that with my multimeter so i use both tools when i'm testing a pressure switch you can also just turn the power off to the gas furnace and you could disconnect the wires from the pressure switch and you could use this particular tool because it has an internal pump and you can use that internal pump in order to determine what inches of water column measurement is needed in order to close the normally open sets of contacts right here you could use this tool basically in order to isolate the pressure switch so if you're confused there's too many hoses going everywhere for that pressure switch and you you think that that pressure switch is the problem you could eliminate the entire gas furnace just for a sec and and just test it individually by itself as a single component with that particular tool right there once again i always connect my multimeter onto this as well going on to the next thing here and we're going to get into some more with the pressure switches and hoses and stuff like that but i just want to kind of keep going another thing that's kind of happened in the innovations of gas furnaces you got to remember that the manufacturers that were designing these furnaces were designing them so that they are safe electrically efficient that maybe the manufacturer could have less components in there or have it be maybe less expensive or whatever that may be and so in this case what this particular manufacturer did is they combined the gas valve and the ignition module into one thing and so this is the smart valve we have four wires here and three wires right here we have a little wiring diagram right here so that you can kind of see you have your 24 volt hot and your common your eft is your electric fan timer output in order to have power going to the hot surface igniter and then for this gas valve to allow pilot gas to be ignited by the hot surface igniter like before any of that's happening you have to have 24 volts on this one tap right here on the smart valve and so you're also going to be going through the pressure switch i just want you to know what this is i've got uh several i think i've got two videos on the smart valve right there so make sure to check those out like the entire function and how it works and everything i want you to be aware of that we have a lot of these smart valves in 90 efficient furnaces around here after you have your your pilot is lit and you're proving that the flame is present at this flame rod and it's it's basically traveling your flame notification signals traveling back through the pilot tube back to the ground of the gas valve and then there's a wire picking it up from the ground of the gas valve into this control board that's underneath of this cover right here in order to determine that you do have a flame present it's using flame ratification in order to determine that and you have your flame is connecting the electrical circuit and rectifying alternating current to direct current basically you might have anywhere from say 80 volts to 180 volts getting sent to this flame rod right here this flame rod does not touch this other piece of metal here that is just that's just the ground right there but what's happening is you have that alternating current is getting rectified and over at this gas valve and maybe it may have two uh microamps for your dc electrical current that is reading for the flametrication process in order to determine that the flame is present so i have videos on that so you can check that out another version of the smart valve is powered with 120 volts and it has an error code status light and so you can see that there's a little uh light indicator right there and so it uses the same hsi the hot surface igniter and flame rod as the other one here we have our intermittent pilot ignition system and so i just want you to see what you would not normally see this is inside of the furnace so you'd see the back of this so you wouldn't be seeing the front you'd be seeing back back here and and not up front but the whole point of this is it is a little dangerous right in order to only be proving the flame at one location right here and if you see in this photo it's actually not really mounted properly and it's dropped down below the burner tube so that that's a safety concern right there right on our direct ignition systems it's safer because it's proving the flame uh across from one point over to the other now on these um on these intermittent pilot gas valve assemblies which can be found on 90 efficient furnace we have our flame roll out switches so you have one here on one side and one on the other side of the combustion chamber assembly now some manufacturers may only have one and that's in my opinion it's not as safe as you having one on each side of the combustion box in fact if i ever have a problem with a gas furnace sometimes i install a secondary one just just to make sure it's safe for the direct ignition control modules some use spark and some used hot surface ignition and so we're talking about 120 volt hot surface igniter right here let's just look this will be the front you wouldn't see this because this would be closer to the heat exchanger area in a gas furnace i just pulled this assembly out so that you could see the the front of it but here you have two rods and you have an eighth of an inch between the two and that's where your spark is occurring at you're basically igniting the the gas over here and the gas has to travel across the burner faces all the way over to the other side and then you have alternating current being sent through that flame rod into the flame and over to the burner retention head when the current is traveling through the flame it's rectified and then you just have a smaller micro amp signal for direct current on that burner retention head and then you use the ground frame in order to get it back to the wire that if you notice there's a little spade connector right here going back to the ignition module so that's completing your circuit for your flame notification so here's your direct hot surface ignition and so you have a hot surface igniter on the one side what you want to think about how this is different than a pilot gas valve is that a pilot gas valve allows a gas to only the pilot and then you have some type of a flame proving process that's usually outside of that gas valve unless you're talking about a smart valve then you have the main gas valve opens to allow the full gas flow over to the burner tubes in this case there is no pilot tube you are just allowing your gas right through it's called direct ignition because you're directly allowing your full gas flow through to the burner tubes in order to light the gas now you typically are only going to have maybe say two or three seconds in order to prove that there's a flame before that gas valve is going to get shut off because that's a lot of gas that's going into the system so you have your hot surface ignitor turns cherry red then your gas valve opens and it allows the full gas flow to all four of these burner tubes at the same time this gets ignited first it travels across right across through this little channel over here and then this is where you're proving the flame with this flame rod and connected to the control board and you're completing the circuit via the flame through the ground wire going back to the control board you have to have gas ignited from here all the way over to here in order for the flame to be proven over on this side as you can see we've had a little issue here and here on this uh furnace i don't know where this was pulled out of but as you can see you had a little bit too much heat on both of these sides right here this is very important i want you to know that the that the flame rod it's not an actual sensor even though it's called a flame sensor you shouldn't be going around changing these out there really is no reason to change out a normal large flame rod or flame sensor in fact i would encourage you to just call it a flame rod all it is is a stainless steel rod that has ceramic around the base and then it has a little mounting clip right here and then a spade connector welded to that that rod so the whole point of this is that what you're doing is you're connecting a wire from the control board to send alternating current via this rod into the flame that is it and so then you have the ceramic piece isolating the ground from that alternating current on direct ignition systems a lot of times you're going to see or you're going to measure a voltage between this big connector and the ground you can measure with your multimeter maybe 85 to 120 volts for your alternating current that's getting sent into this now if you put your multimeter in series that's how you can check for your flame notification uh but we'll get into that in a little bit we have our direct ignition gas valve you see there's an on off button right here and you just have your your your gas in and your gas out and then you have right here is a vent and then right here is where you can adjust the gas pressure there's a little spring in there measuring the inlet and the outlet of the gas valve so this is a direct ignition gas valve you want to know what input gas there is going into that going into that furnace you want to know that the gas line is sized properly because if the gas line that's supplying the the furnace is undersized and when that furnace turns on the the actual pressure and volume in the pipe lowers or you turn on say a a water heater or a dryer or whatever else in the building and all of a sudden the pressure lowers at the furnace that can cause issues so you need to be aware of that especially if it's like an intermittent problem right here you can see our natural gas input is normally anywhere right around five inch water column to eight inch water column so what's that about a quarter of a psi it's really not that much pressure natural gas outlet uh pressure is usually between three and three point eight inch water column and so you're going to set that with your along with your combustion analyzer in order to try to get your your most efficient burn it's maybe 3.3 it may be 3.5 inch watercolor maybe you know whatever in there you can use a standard ratcheting surface wrench the same one that you would use at the service valves on an air conditioning system in order to take out the little allen screw so you want to first turn off the gas at a gas furnace first turn off the valve and then be able to take those taps out in order to measure your pressure you could also measure your inlet gas pressure over at the the cap at the outside of the unit like on the drip leg if you have an adapter for that you want to measure what your outlet gas pressure is and be able to adjust that for efficiency and to know is the gas valve sputtering like do you have a troubleshooting problem and the gas valve is not acting the way it should you know and you can see maybe a sputtering of the flame that could be an air problem that could be a gas valve problem it could be several things now lp inlet is normally about 11 to 13 inches of water column and that's about a half of a psi lp gas outlet maybe anywhere from say like 9.5 to 10.5 inch water column and that's for a single stage gas valve a single stage direct ignition gas valve you don't want to just set it at 10 for for no reason you want to set it at whatever the manufacturer is specifying for that particular unit that's just normally what it's at so don't go by this as far as setting your gas pressure make sure you're following the the rating plate of the gas furnace it's usually on the cover of the furnace as far as your pressure what to set the pressure's at for gas furnaces they normally are coming as natural gas and then you can convert them to lp by changing the orifice out you can change the spring out in the gas valve you may have to change your combustion error and you're going to have to set the gas pressure while that system is running you want to put a sticker on it let everybody know hey this has been changed to lp you're going to do your combustion analysis to to verify that you got a clean burn so you're going to want to do those things anytime that you're converting from natural gas to lp silicon carbide hot surface igniters some people are asking why why do they look like this so the whole point is that the gas the fuel gas is traveling kind of through this and around it you're increasing the surface area on that hot surface igniter to help with ignition you don't want a late ignition you want an immediate ignition and the silicon carbide though they don't last as long as the silicon nitride sometimes because of the way uh gas furnace is designed the combustion chamber and stuff like that you may just want to replace it with another silicon carbide because of the surface area because of how it's able to kind of get over the whole area where the gas is flowing over you can replace that with a silicone nitride you just got to be aware of the positioning of that silicone nitride hot surface igniter but we'll get into that in a bit you do not want to visually inspect a hot surface igniter to see if it's correct you want to test it with your multimeter while it's still in place one of my first service calls i got sent to and i was visually checking a hot surface igniter i mean obviously this is when i just had started out nobody had told me what to do unfortunately i wish i wish i did know a little bit more at that time and i didn't i pulled that hot surface igniter out i cracked it no good i had to install a brand new hot surface igniter in there and that wasn't even the problem like i'm saying just disconnect the plug so there's a plug for the hot surface igniter and what you want to do is you can just turn the power off to the furnace and you can check the electrical resistance of the hot surface igniter so it may be anywhere from say 40 to 65 ohms of electrical resistance and that means that that hot surface igniter is still good and that's for say 120 volt hot surface igniter the 24 volt hot surface igniters are going to be a different ohm range resistance range if you ever measure ol when you're checking your electrical resistance on the two wires that lead to the hot surface igniter that indicates that that hot surface igniter is bad it's cracked and when you do finally pull it out then you can actually see where it's usually white at or maybe broken so that's what happens when they fail they end up breaking and stopping the electrical circuit right there testing a silicon nitride hot surface igniter here you see we're reading 48 ohms and just so you know if it's still hot the electrical resistance is going to be higher but in this case since we're not reading ol we know that the hot surface connector is still good any time that you have this you want to have that flat blade uh facing the the burner tube because you want more surfaces more surface area not less surface area uh in front of the gas in order to ignite it here we have a 80 efficient package unit and so when you're looking at these these take a lot of abuse and the whole point is that they're outside all the time and so a lot of components rust you'll get spider webs down here and insect problems and just they're just rotting we have a lot of issues the metal uh inducer motor the capacitor the the combustion chamber the whole thing rusting at the burner retention heads this right here is very rusted and so you end up having to replace multiple things when you're rebuilding a package unit may not benefit you to just do one thing at a time it may benefit you to just kind of go through and clean clean it up most of these package units you're going to see they're going to have a spark ignition going to be a direct spark ignition usually that you're going to find in these 80 efficient package units outside on our blower motors you're going to typically see a permanent split capacitor blower motor on the any of the 80 efficient furnaces the older ones and older 90 or 92 percent efficient gas furnaces but then we kind of moved on to other blower motors as well but these were very prevalent in the 80 time period some 80 efficient furnaces will still have a fain limit switch so you need to be aware of that some units i used a sequencer in order to control when the blower motor turned on so it's waiting for the heat exchanger to warm up before the blower motor turned on and some units especially if there are very compact units have used a sequencer in order to accomplish that task so make sure you know how the sequencer works and i have a video on that as well so you can just look up say on youtube ac service tech sequencer and you'll find the video for that so here is a control board uh so during the whole evolution of these gas furnaces even on 90 efficient furnaces you're going to start to see the furnace control boards being integrated but here we have a fan timing furnace control board and so the whole point of this is that it does control the inducer motor the power to the inducer motor but it does not control the ignition you need to know what you're looking at so if you have a problem with ignition and you go and replace this board it's not going to do you any good at all so you got to know what it is so right here we have our integrated furnace control board this is basically taking our fan timer board and our ignition module and making them one one thing that's why it says integrated for the furnace control board so it's ifc and these have led status code lights and of course some of the ignition control modules had led status code lights you can see our flame rod right here is just sitting there next to our ifc and both of these ifc you see these large blocks so the black blocks it may be gray blocks white blocks those are relays they're direct current relays on the control board and anytime you have those are typically for uh a furnace that has psc or shaded pole inducer motors it's usually psc so you're just switching power on and off to the blower motor or on and off to the inducer motor here you have the uh the limit switches right here and so the ifc constantly monitors to see is one of these uh electrically open they should be electrically closed all the time and over here you have your flame roll out switch so you can you know a flame rollout switch is only manually reset by a button but our regular thermal limit switches right here they will automatically reset and they use a little bi-metal disc in order to uh pop the electrical switch up and open it or it's going to naturally sit in the closed position this one right here reaches further into the plenum part of the gas furnace next to the heat exchanger in order to determine you know is this furnace overheating and that's the whole point this one right here is actually on an older 60 efficient furnace that's an older style but these are fairly common any one of these three right here are fairly common this one uh somewhat common and then you always have your different versions of your flame roll out switch measuring safety switches so we have a video three ways to measure a switch you know when you're working on the hvac system so make sure you check that out here we have two two ways you could turn the power off to the furnace you could disconnect the electrical wires and then just take a resistance reading across the switch if you read 0.0 ohms of electrical resistance then your switch is good and it is closed presently and not connected available the switch over here on this right hand panel right here if you were to to do that and just you know you have to imagine if you did have your two wires still on there if you measured across a switch zero volts but you do know that you have 24 volts supplying it then that means there is no difference in the voltage across the switch meaning that if this switch was open and you measured voltage from one side to the other side you would read 24 volts if it was electrically open in this case it's not it's reading 0.0 volts so that means that that switch is electrically closed if you did have the wires attached and you did have power to it i prefer jumping around in the furnace by putting my multimeter on voltage and taking one of my probes and putting it on the ground or the common on the on the furnace control board make sure that the door switch is closed and then you can take your other probe and just kind of put it on each of the switches on both sides you're kind of playing hopscotch a little bit you're just one okay i read 24 volts i read 24 volts there next switch i read 24 volts and then on the other side of the switch oh all of a sudden i don't read it anymore that means that that switch is the one that's the problem because you got to remember you have like you may have like four or even five of these switches inside of a gas furnace so you may have temperature limit switches uh going to the control board and then you may have your flame rollout switches sometimes they're all together in series and so you want to check each one individually and so you can do that real quickly so make sure to check that video out where you're just putting one probe on the common or the ground because remember on a gas furnace on say 80 any 80 or 90 efficient furnace or higher your common for your transformer is connected to the ground frame so you could just connect it at a good ground on the furnace anywheres and then take your other probe and try to measure for your 24 volt power remember your 24 volt power is anywhere between 24 and 29 and a half volts the ifc sends alternating current to the flame rod and measures direct current so dc microamps on a dedicated ground from the combustion box we have our little animated picture over here and so hopefully that is a good indication where the flame or a good picture of how the flame is completing the circuit what we would do is we turn the power off to the furnace put our multimeter in series between the flame rod and the wire going to the flame rod and we're going to be measuring direct current micro amps okay even though we are supplying alternating current to the fleeing if you remember when i was talking about the uh ignition control modules we usually check that on the ground of the of the furnace and we're checking it between the ignition control module and the ground wire on direct ignition systems you're checking it on say the supply side you're checking it on the wire before it gets to the rod once again just put your multimeter in series i have a couple videos on flame rectification so you're aware of how to do that and how to measure for that in this case in this image right here we're measuring 2.4 microamps you you want to have somewhere between say 2 microamps and say 10 microamps you may measure 12 you may measure four i mean really it'd be better if you had higher than three but some furnaces may have a little bit lower than than three maybe 2.5 2.6 2.3 so really you want to make sure it's up above too if you have an intermittent problem uh with your gas furnace and you have an led status code light that's indicating hey you have a flame ratification problem you're going to be measuring that you know and you're going to notice hey maybe my signal is is low and so you want to see is that flame in engulfing that flame rod you know what you're going to want to do is clean the flame rod with unsoaked or non-soaked steel wool you want to clean it and make sure it's clean with the power off to the furnace because that rod is going to have power on it all the time any residue any carbon buildup on that rod or any rust on the burner retention head is going to act like electrical resistance in this flame rectification circuit so you want to clean those things you know you may have a problem just right here at the face of the burner retention head where the flame sits at and that may be the problem there's two ways that you can test the ground circuit so one is electrical resistance so with the power off to the gas furnace what you can do is you can clip one alligator clamp on your multimeter over at the the back of the burner burner tube right here so you can clip right here or clip it on the actual ground area where say the wire attaches to and so the other probe is going to go to where you find the green yellow wire going to the control board that is where the control board is attaching to the ground frame some control boards have one of the screws that goes from the control board to the frame and that's the ground wire but more often than not you have a dedicated ground wire that goes to a plug and you just got to follow it trace it back and you're also going to notice that that attaches to the electrical gas valve as well that's actually the common and so that's why we're not checking it on the ground side we're not checking the flame notification signal on the ground side because you can mess up basically the power going to the gas valve by trying to put your multimeter in series on that side that's only for direct ignition system so what you could do is you can check for electrical resistance between the the burner tube all the way back to where the control board is trying to to measure the micro amps at if you have any electrical resistance between those two points that's going to lower the signal down to a lower level it's going to act as electrical resistance to the flow of electrons and so it's going to mess the signal up so if you read an oom of electrical resistance you have a problem you need to check your your ground wire your your make sure that there's no paint or anything like that make sure that you have a clean surface make sure you kind of sane that down where the dedicated ground wire is attaching to the combustion chamber at you know there's a problem somewhere as then but you want to read 0.0 ohms over electrical resistance you might have 0.1 ohms you don't want 0.2.3.4.5 ohms of electrical resistance and guess what it's not going to matter a hill of beans for you to go testing all this stuff if you cannot take your two probes of your multimeter connect them together and read zero ohms of electrical resistance sometimes your probe wires on your multimeter are bad you always want to go ahead and test your multimeter first before before using it so if you are connecting them like this and you're measuring electrical resistance right now and we measured 5 or 0.5 ohms or even 0.3 ohms we have a problem we should be replacing our our probe wires for new ones you know it could be a problem with our multimeter but very likely it's these these wires right here especially if we have alligator jumpers on here so i just want you to be aware of that the other test that you could do is a voltage drop and so what this is doing is with the power onto your gas furnace after you've already clipped onto your ground wire here and your common wire right here it's going to complete the circuit all the way back at the breaker box and so if you uh were to disconnect the common for this furnace with like say you're trying to turn the power off to the furnace and you disconnect the common somehow going to the the breaker box for your power supply you're not going to read anything right here but if on 120 volt furnace if you measure between l2 your common wire and your ground it's going to complete the circuit all the way back where it's connected inside the the building's electrical breaker box and come all the way back and you should have very close to 0.0 ohms of electrical resistance if you have ol then that means likely that your ground wire is disconnected somewheres and that could be a big problem if you had like one two three ohms once again that's a that's a big problem and that can affect your your micro amp signal going back onto the ground of this gas furnace and you're going to have an intermittent problem a lot of times and so you need to make sure that you are supplying your gas furnace with good power with a good ground going all the way back to the breaker box the integrated furnace control board has led status code lights so when you're walking up to a gas furnace when you're going to service it you want to pay special attention to the little peephole on the furnace and read the status code light however it may be reading a lockout error code and so you're still going to have to take the panels of the furnace off and then you're going to have to recall the prior error codes and each furnace may be a little bit different in order to recall those error codes but you want to go ahead and do that because that's going to tell you where to start your troubleshooting at it's going to tell you say if it has like say a pressure switch problem it's either a pressure switch related problem it doesn't mean that the pressure switch is bad it could be water in the exhaust pipe a clogged condensate drain it could be a clogged port for the pressure switch but it could also be a bad inducer motor or a bad wheel or the wheel is missing some of the fins it could be multiple different things so remember that whatever error code is flashing it's either that step in the sequence of operation or the earlier step so you always want to think about that when you're troubleshooting on the gas furnace it'll tell you uh it'll tell you the possibilities of what could be wrong right here but you you want to know that yourself you don't want to be dependent on this stuff you want to kind of be thinking about that already 90 efficient gas furnaces so we talked about it a lot already but the pvc exhaust the condensate line coming off of them there's no louvers it could have one or two pvc exhaust pipes and by the way if you're installing 90 or higher efficiency gas furnaces you want to use two pipes you don't want to be drawing the building into a vacuum by taking combustion air basically stealing combustion air from within the building and putting it into the furnace and then just exhausting it because what's going to happen is you're going to be pulling in outside air through the cracks in the windows and doors and stuff like that back into the building and once again your building is going to be under a vacuum you don't want to do that you want to take a dedicated combustion air tube all the way to the outside and so you can even do that with one hole through the building using what's called a concentric kit 90 efficient gas furnaces have a primary and secondary heat exchanger our secondary one is a water heat exchanger and you can kind of notice that because it's a tube and fin or most furnaces are tube and fin at least and then your primary heat exchanger is just your your standard one like you would notice on a 80 efficient furnace and then you have your box right here where the two join at so really what you want to think about is your secondary heat exchanger is the first one in the air path for your com for your conditioned air in the building what's going to happen is this heat exchanger your secondary one is going to be at a lower temperature because your your flame is basically starting over here and your exhaust gets pulled in here it's going to be hot hot hot hot right but it's going to be lowering in temperature as you're exchanging heat with the conditioned air that's blowing around the heat exchanger it's lowering in temperature lowering in temperature lowering in temperature so much so to the point where the water in the exhaust is condensing in the tubes and it's running like just along right in here in this uh secondary heat exchanger but it's going to be lower in temperature lower in temperature lower temperature and then it's going to be trickling out of the furnace into a condensate trap naturally this heat exchanger which is a secondary heat exchanger is going to be the first one in the air path so the air is going to be absorbing heat from the hot but yet lower temperature heat exchanger and then it's then going past the hotter heat exchanger and it's absorbing more heat and then going into the building and so basically if you had 70 degree air down here by the time it gets past the the secondary and the primary heat exchanger it should be maybe 50 degrees higher maybe at 120 degrees before it enters and gets distributed through the building so as a result of cooler exhaust temps or lower temperature things aren't cold that's just a feeling we have right but as you have your lower temperature exhaust you have higher uh gas efficiency because of that you're going to have your lower exhaust temp and plastic inducer motor housings so as a result of your lower exhaust temps you're going to have a higher efficiency furnace with a plastic inducer motor housing and the whole point is that the exhaust temperature is low so we can make the inducer motor housing and wheel out of something that can withstand or withstand the temperature and withstand the condensing water and so it's not going to rust you're always going to notice these plastic inducer motor housings on 90 efficient furnaces you may notice some that are stainless steel but they're primarily all plastic because it's hey it's the lower cost right 90 efficient furnaces use pvc tubing for the exhaust along with the intake we already discussed that 90 efficient uh furnaces require a condensate trap without a condensate trap you're going to not be allowing the water to trickle out of the furnace the whole point is that your low low pressure area and your say high friction is going to stop right here at the trap once the water gathers in the trap it's going to be able to just trickle out naturally out of the furnace we had some of these larger uh condensate traps back when now they're making them so that you can see into them and see all the gunk or see if they're clogged so that's that's kind of nice these get clogged quite a bit so this is a lot of times what the problem is on a 90 efficient furnace this is part of the preventative maintenance it's cleaning the tubes it's and make sure that the tubes are disconnected from the pressure switch by the way it's cleaning the condensate traps it's cleaning the condensate pump it's all of those things and even the tube that is leading off of the condensate pump if you have one there's a little check valve there and that needs to be cleaned so there's a lot of different things when you're talking about preventative maintenance on a gas furnace and depending on what your company uh does and how much time they allow you know every company is going to be different in the amount of preventative maintenance that they're performing often there is two pressure switches in a 90 efficient furnace one is going over to the condensate trap and the other one is going over to the inducer motor housing you can see there's one here and there's another one right behind it just uh two of these pressure switches with a single port and on this case uh in this case the backs are not connected on these two pressure switches so this looks like a jumbled mess right so we have three furnaces right here and you have a bunch of different tube layouts that are connecting from the inducer motor the combustion box gas valve pressure switch or multiple pressure switches i just want you to be aware of what's happening right here so over on the left this furnace has two pressure switches one is connecting to the trap one's connecting to the inducer motor while that system is running they should both be closed this one right here this one in the middle is taking a differential and and remember even though we have two patch switches over here is taking a differential of pressure we're lowering the one side uh worth of pressure while the other one's atmospheric even if you have a single port pressure switch in this case you have a tube on the front of the pressure switch and a tube on the back of the pressure switch the back of the pressure switch is monitoring the condensate trap while the front is is monitoring the combustion box so the pressure inside the sealed combustion box as well it's actually teed off over to the atmospheric port of the the gas valve so that when this gas valve is allowing pressure in here it's it's utilizing the atmosphere atmospheric pressure within this box in order to allow the pressure to be correct here you have a two port pressure switch it's taking a differential the back side on this should be lower than the front side pressure on this furnace right here you have one pressure switch on the bottom with one tube connecting over to the condensate trap and then you have another pressure switch right here and you have a tube that is connecting over to the lower part of the inducer motor and then it has another tube on the other side that's connecting over to the combustion box and of course anytime you have a sealed combustion box you're going to have a tube connecting over to the the gas valve and so it's going to always go over to that atmospheric port if you don't have a tube there you usually have like a set screw with a little hole in it or a plastic piece that's there that's going to be allowing atmospheric pressure at that potential uh part of that diaphragm right there for the gas valve this one is still taking a differential it's just taking a differential between the atmospheric pressure at that point at that part of the furnace like inside you know the frame of this furnace which means it's going to be the same as the outside of the furnace but and then you have the other tube that's going over to the inducer motor and that's going to be lower in pressure and so you got to remember that a pressure switch is always reading a differential even if it only has one port on it it's going to have atmospheric pressure on one side and then it's going to have the pressure tap on the other side the pressure tap side is going to be the side with the spring and when you're inducing motor turns on you're lowering the pressure in that area beyond the spring pressure and you're allowing the switch to so to mechanically close and then it's going to allow your electrical current across the switch you know in a gas furnace in this area right here we have a sealed combustion box anytime you have that the gas valve has to be connected with a tube going over to the atmospheric port of this gas valve so that it can maintain the proper pressure going in to that sealed combustion box what you're going to have here is that on the front of this pressure switch you're going to be connected to the combustion box and it's taking a differential between there and the condensate trap the condensate trap is basically almost a direct pathway over to the inducer motor so that's going to be the the the lower pressure side i want you to know that on a pressure switch when you have two ports it's reading a differential right and they might be marked with a negative and a positive right here i just want you to know that both of these pressures are lower than atmospheric pressure it doesn't mean a positive pressure the negative port is lower pressure than the positive port it just means a differential no positive pressure a furnace with only one pressure switch and a combustion box is reading a differential and this is to test the pressure switch while connected to the system and in order to test the pressure switch while connected to the system we want to measure the water column reading on both sides of the pressure switch so it's very important to know that on a pressure switch like this there's no point in teaming into the tube on one side of the pressure switch you need your pressure readings on both sides it's going to look something like this you're going to have your little brass tees or your plastic t's with the power off you're going to t in either read this as a differential or you could take your your one pressure and subtract that against your other pressure in order to find your differential but that's why it's it's nice to kind of have a dual port water column manometer and by the way we can't really get by with the with the non-digital water columnometers anymore because we have gas furnaces that are running at such a low water column pressure that you wouldn't really be able to see it on the dial anymore it's not very helpful when you have a a water columnometer that's just a dial type like a compound gauge you really want a digital version and you want to make sure that you're zeroing it out before using it and make sure that it's calibrated and functioning properly like i said before if you were confused or you wanted to confirm that a pressure switch was the actual problem what you can do is while the pressure switch is still mounted in the in the furnace and it has to be mounted up like this not like this while it's still mounted in the furnace you can and to power off disconnect the electrical wires you're going to attach your in this case it's a field piece sdmn6 you're not going to have your your tube on this side you're going to have it on the pump here in the middle it's wide together and you're going to connect that over to the negative port of the pressure switch so you're not going to be connected to the positive you're going to be over at the negative where the the spring is and then you can turn your pump on and keep turning your your water column your water column pressure to a lower lower pressure than atmosphere atmospheric until your pressure switch electrically closes and you're going to measure that with your multimeter by reading the electrical resistance across the electrical contacts and so that's how you can determine if that pressure switch is in fact the problem so once again make sure to check out our newest video on gas furnace pressure switches so now that we've gone over that we have two stage gas furnaces so you may run into some of those so you could have a multi-speed psc blower motor you could have a two-speed inducer motor that in this case is a psc you're going to have an additional pressure switch because remember your inducer motor is going to be running at at two speeds now not just one and you're gonna have a ifc with two heat speeds you know for your uh powering your inducer motor and you're gonna have a two stage gas valve and so this is a direct ignition gas valve the easiest way to determine it is just by looking at the gas valve you see two brass screws so you know there's a medium and a high or a low and high and just remember that most of these two speed gas valves you're going to have to be powering both medium and high on this to open both of those up in order to allow your direct ignition to occur on your high speed if it's just medium then you're typically just going to have your medium speed powered once again early 90 efficient furnaces had multi-speed pse blower motors with a capacitor but now we have ecm variable speed blower motor so the first thing that came out was more of the variable speed and you may notice like a 16 pin uh connector on the module so this black spot right here this black section of the motor that's actually a motor module on an ecm blur motor up here this blue gray part that's the frame of the blower motor and inside you have a three phase wound blower motor over on this one right here instead of being a 16 pin connector you're gonna see just a four pin connector and a five pin right here with these variable speed ecm blower motors these are also known as constant airflow if you ever hear these weird terminology you know kind of thrown out there constant airflow what they're really talking about is the variable speed blower motors so these don't have the 24 volt signals to turn on and turn off however the manufacturer has made these so that you could test them with a 24 volt signal you may have a a tester tool that you could use such as a techmate pro in order to check this with just a 24 volt signal so that that particular tool right there it has a 16 pin connector and it also has a four pin connector and you're just powering it with 24 volts on the certain pins just to see if the inducer motor is even going to turn on but you may also have other problems with a variable speed blower motor such as the blower motor doesn't shut off you know you could have it ramping up ramping down ramping up ramping down a lot of times that's due to some airflow problem such as a clogged filter or something like that like a completely clogged filter has done damage to that ecm blur motor due to the high electrical current from that inducer motor module allowing more current to the motor in order to overcome the friction so anytime you have an ecm electronically controlled module you're going to have a communicating control board and so instead of having the large black relays on the on the control board on the integrated furnace control board it's going to just be sending signals and talking with the module so you're going to have the module talking back and forth with the ifc control board once again in order to tell if your motor is the problem you could just disconnect the communication wire connect the techmate pro and see if the inducer if the blower motor is actually going to turn on or not if the blur motor does not turn on then the blur motor module is the problem a lot of times you're going to have to buy the module and the motor together and a lot of times the regular motor shell is not going to be damaged so this part right here is usually not going to be damaged unless a capacitor blows inside there's usually a couple capacitors in here you have a bad electrical surge or a high or low uh voltage at the building you could have one of the capacitors below and it'll squirt fluid into the the motor in that case you definitely want to replace that that motor but you also want to think about like motor bearings and stuff like that you might as well just go ahead and replace the whole thing even if you only have to replace the module okay so here you see the modules you can visually inspect them so right here you have a burnt capacitor it's actually mushroomed just like you would see on a a run capacitor off of a air conditioning unit or something like that it's leaking fluid it's obvious that it's bad you could have right here there's like a round pill type ptc thermistor it's actually acting as a current limiter in this in this instance and that is is burnt off and bad it's possible to just replace that particular item if you soldered a new one in but really this module is bad in this instance and over here the uh you can see for that ptc thermistor it's actually melted uh the the rubber right here or the silicone you can see that this one is burnt and bad i don't know if you can actually see it or not but the whole point is that you can you can visually inspect it a module you can smell it if it's burnt you can test it with your techmate pro tester so there's three different ways to kind of determine if a module is bad and you can just take electrical resistance readings on the rest of the motor it's just a three-phase motor so each pair should be equaling the other two pairs when you're checking electrical resistance with a multimeter we have our variable speed inducer motor was introduced and this contributed to increased electrical efficiency and so you match a ecm variable speed blower motor and a variable speed inducer motor with maybe a two speed or a three speed gas furnace ecm multi-speed motors you're going to hear them hear of them as either ecm multi-speed or ecm constant torque and so really that just means the same thing these are pretty easy to troubleshoot really you're gonna have your your power in just make sure that you have your 120 volts or your 240 volts in and then you just measure on on the tap that's supposed to be being powered with 24 volts hey do i have 24 volts there if i don't have 24 volts there then we're not really calling for that blower motor to turn on if you do have 24 volts on one two three four or five and it's programmed to run on all five of those speeds and then that blur motor is bat but just remember that the off even though there's five taps there may only be two taps that are programmed but the whole point is that the other one should still be on default so it should still turn on if you have 24 volts on one of them that's the whole point your common for your 24 volt is going to be up here and then you're going to have any time that you supply hot on 5 4 3 2 or 1 taps that blur motor should turn on so it's very easy to determine is that blur motor operating the way it should or is it not if you're looking at like say like a gen tech it'd be like x13 that's that's kind of what we're talking about the broad ocean models they have they have ones that usually have a plug like this the x-13s usually have a plug on the side of the units here's another example of a broad ocean one where it just has the the wire sticking out and then it has the wiring diagram right here on the side on really high efficiency gas furnaces you may run into units that are a three-stage gas valve or three stages of gas and it's really made up of a two-stage gas valve with a third stage and the third stage is the lowest stage so this will be considered the low and this is the medium and this is the high so you could have that you could have a modulating gas valve so you want to be aware of all these different types of gas valves that you could potentially run into you have your control board up here on the top and this is going to be communicating with your ifc your integrated furnace control board now here's just a rundown of a bunch of different gas valves kind of starting with the earlier gas valves all the way up to say a three-stage gas valve so you have a combination gas valve here you have a pilot ignition gas valve you have a 120 volt smart valve right here you have a direct ignition instead of a pilot ignition and here you have a two stage direct ignition gas valve here you have a three stage ignition uh direct ignition gas valve you really want to be aware of what you're looking at once you open up that cover on the gas furnace and if you are unaware of one or multiple of these versions those are the ones that you want to target and you want to start studying and look at you know you can look at them on youtube you can you can just type it up in in your search engine and read up on them you can do some manufacture training so you just want to be aware of what you may run into so that you are an effective troubleshooter out in the field and that you're safe as well so here is a bunch of different pressure switches so here's a single port here is a two port here's another version of a two port and in this case you have three terminals right here one set of normally closed contacts and one set of normally open contacts once you lower the pressure on the spring side the normally open contacts are going to close and normally closed contacts are going to open here you have another metal type where it's just a single port and you have two tabs here's a two port and you have three tabs right here you're also going to notice a little tiny hole right here that's the atmospheric port none of the sides of the pressure switch are fully sealed you're always going to have a tiny tiny little port in order to when when you turn the power off to a gas furnace or the inducer motor loses power both of these chambers right here should quickly go back to atmospheric pressure so that the pressure switch can open up the contacts again so here is just several control boards so here we have a integrated furnace control board and since you don't see these large black blocks here the direct current relays this one is for ecm inducer motor and ecm uh blower motor this particular one right here this is just a standard ifc and you can tell that because it just has these switches right here so this switching mechanism right here is for your air conditioning and heat blower speeds and then here this little black box is going to be allowing power to the inducer motor over here you just have a fan timing control board and here you have an ignition control module so you're just going to want to know what the difference is between these things and here's just a picture of a dual water commonometer with a pump this is the sdm n6 and it has the pump tap right here in the middle and then it has the uh one right over here on the side you want a dual water commonometer regardless of whether you have one with a pump or not for checking pressure switches you're going to want to have a dual water commonometer not only for checking gas pressure and your water column measurement at your pressure switch but also for airflow as well so you're going to want static pressure uh tips or probes basically you have a little magnet here and you can insert this into the the airstream and you're you're measuring your static pressure so if you have a high total external static pressure you're going to either have a problem on either the return side or the supply side whichever one is higher you're really going to want to have this tool in order to do multiple types of diagnosing on a furnace you're going to want to have a multimeter so a digital multimeter with an ac amp clamp you want to want to have it be able to read capacitance for testing capacitors you're going to want to be able to read micro amps for direct current and you want it to be true rms you're going to want jumper wire so alligator jumper wires you're going to have also you're going to want probably magnet jumpers to be able to jump inside the the thermostats and so the magnet will hold it in place it's got little neodymium magnets then you're going to want a door switch magnet as well so you're not going to want to play around with tape every time and you can get magnets like free magnets right out of like a microwave if you want like a scrap microwave but you can buy the little flat neodymium ones that will sit sit in there even when you put the furnace door back on but i like the larger magnets this way i remember and know that that magnet's still in there it's not allowing the door to fully go on there but anyway you could have a multitude of those but you're going to want a magnet to hold the furnace door switch in the closed position mechanically you want to have a combustion analyzer this is the residential model so you're going to want to have that in order to set your gas pressure and to test if you have maybe a crack in the heat exchanger if you're doing a lp conversion from natural gas or you're just you know you're just commissioning a new furnace so you're going to want to have a combustion analyzer it would be good to have a carbon monoxide detector so that you can have that on your body if you're going into an equipment room you don't know if you're just breathing in a lot of carbon monoxide while you're there so that's kind of more of a danger thing could also be putting this over at the supply registers and then you can turn the furnace on hey is does my carbon monoxide level reading rise you know while the furnace is running and that would indicate that hey there's probably a crack in the heat exchanger or the heat exchanger has pulled apart at the right where the heat exchanger meets the the one plate app it could be that it could be a multitude of different things the other thing is you don't want to be trying to utilize that at a supply register like see near the kitchen where you may have a little bit of carbon monoxide from the cooking appliances but really if you're going to tell somebody they have a crack in the heat exchanger you want to be able to visually find it you're going to want a a video scope in order to do that you may go through the heat limit sensor in the plenum area next to the heat exchanger you could take that out and you could look in there you could drill a hole up in the just a flat metal plate near the the evaporator coil and look down there you could do several things as far as trying to locate it it is hard you could stick it in through after you take the the burner tubes off you could stick it through there inside the heat exchanger itself if it's cooled down you do really want to get a visual picture for the building owner if at all possible in order to really show them they have a crack in the heat exchanger and it is hard i get it this is a st4 and we have two k-type temp sensors and so with this you can take a zip screw out of the return and supply you can then measure your delta t you can measure your temp rise for your gas furnace you want to make sure that your temporize is not increasing increasing increasing meaning that your blower speed is too low or you're over firing so that's important to have once again you can just slip these right inside of a zip screw hole and then just when you're done you can just put your zip screw back in your techmate pro for being able to troubleshoot ecm variable speed blower motors once again if it's an ecm multi-speed or constant torque blower motor those are a lot easier to troubleshoot and i've got plenty of videos on ec and blower motor troubleshooting so just look up ac service tech ecm troubleshooting or just ac service tech ecm blower you know and that'll take you to those videos on youtube i hope this video helped you and if you want to learn more about hvac make sure to go to our website over at ac service tech dot com we also have a air conditioning book the refrigerant charging and service procedures for air conditioning so we've got that a thousand question workbook quick reference cards but i just wanted to kind of give you just a general idea of some of the components you may run into in gas furnaces and this is not a all-inclusive list either there's other things like a mercury sensor there's a three wire ignition there's all kinds of different combinations and things that you can run into in the field and i just want you to be aware and so that you can kind of start to learn and plug those holes those knowledge holes hope you enjoyed yourself and we'll see you next time at ac service tech channel

Channel: AC Service Tech LLC

Views: 693,306

Keywords: acservicetech, repair, maintenance, how to, fix, hvac, hvacr, how do you, test, ac, service, tech, check, measure, read, superheat, subcooling, refrigerant, procedure, voltage, charging, temp, multimeter, freon, hvac class, hvac school, hvac training, Gas furnace, Propane, Natural gas, Operation, Service, Sequence of operation, Gas valve, Ignition, Heater, Gas heater, Forced air gas furnace, Central heater, Thermostat wiring, Ifc, Furnace control board, Hot surface ignitor, Hvac course, Furnace class

Id: PlA1kBz2kHA

Length: 80min 49sec (4849 seconds)

Published: Sat Apr 09 2022