Electrical Troubleshooting! Finding 8 Electrical Faults!

this is craig magliaccio from aec surface tech and today what we're going over are eight troubleshooting scenarios which we're going to diagnose using our multimeter on our electric training board for hvac students so if you're not aware we have the this whole board all the parts the dimensions how to build this step by step over to our website at aecseverstick.com in the articles and the resource section so now we're going to get started with our diagnosis [Music] after i set a fault in the board i don't have the students wiggling the wires or removing faceplates to visually find the problem i always have them use the multimeter in order to find the problem and then to show me it with the multimeter we are also using a gfci plug right here and we're using it as an on off switch and for extra safety during the process and now we're gonna get to our troubleshooting scenario one so before we get started right now i have the power off at the gfci plug and i'm just going to use these buttons to turn it on and off right here is air conditioning mode so once again the power is off but if we turn it on cooling and press the temperature down what should happen is our contactor should suck down and we should have power at the plug so the fan and light will work and then if we were to just turn the fan on then we should have power to the fan and so this is the fan and the sequencer turns the fan on but only during heating mode so if you were to turn this to heating mode and this remains on auto and you turn the heat up then we should have our light lit and then after the light lights uh lights up then the fan should turn on and then when we turn power off the fan should continue to run for a little bit just like on a furnace and then it'll shut off uh by itself and that's all due to the sequencer right here if you want to learn more about each of these components i've got individual troubleshooting videos in the description section below now we're going to get started we already have our multimeter set on voltage for alternating current and you can see the squiggly line that's the sine wave and so we're going to turn our power on for our first troubleshooting example now right now you can see our thermostat is set on the off position so the only time the fan should be running is when the thermostat's on the on position so if we do this and the fan should be running in this case we're not even doing that so that's a problem so let's take a look inside here oh you just saw that the fan turned off when i removed the face plate so this is likely our problem let me just explain to you what is going on here in the thermostat we have a jumper between rc and r right here so we just have our one red wire so our red wires coming from our transformer going through our little breaker over to our wiring block right here into the thermostat so this is our 24 volt power in and our blue wire that is our common wire and that goes back to the transformer and so when fan turns on r so r and g touch in the thermostat right in the face here and when uh for r and y when those two touch that's for cooling mode and what's going to happen in cooling mode is you're also going to have r and g touch as well now for heating mode you're going to have r and w touch and so you can see the weight wires on w yellow for y and green for g red for r and we typically use blue for our common so what's happening right now is that we should not have any power between uh our common and our g so you see we have zero volts we should have 24 volts which is actually right around somewhere between like say 28 29 volts we have 28 volts between our common and r we should always have that as long as our transformer is good we have power and our breaker is not popped when we put our face in you can see that if we measure from common to g we actually have 28 volts when we shouldn't that means that the r and the g are touching in the thermostat face so the thermostat face in this case is the problem now that we've replaced our thermostat face we're going to turn the power back on again and now we're going to test the thermostat make sure all of our settings work so we're going to turn our fan on first so that's good we can turn our heat on looks like heat isn't working uh so let's uh we'll test that out and then let's also test our air conditioning which is cooling so you know there's a five minute delay in the thermostat and so it says cool on and it's flashing and so what we would typically do in the in the classroom is i wouldn't have the students wait for that five minute delay what i can do is i can just take this off and then we can jump from r to y so this would represent our outdoor air conditioning unit so this would represent the compressor and the condenser fan now also what's going to happen is in air conditioning mode this indoor fan is also going to be running but since we're we took the face off we're just jumping from r to y instead of from r to both y and g all right so anyway we know that our air conditioning works our fan works and we know that our heat does not work and so let's just jump her from r to w so we should have let's just check from our baseline again from common to r we should have 24 volts which we have 28 volts now and we're jumpered over here or to w now if we go from common to w which is our weight wire we have zero volts so we know that we have a problem from the thermostat over to here because we should we should have power right over here you know so we know that we have an issue and so now what we can do is we can go to our resistance and we're going to turn the power off to this assembly and then we're going to check a resistance value of course this is not going to be like in real life basically from here to here we should have zero ohms just like on the green wire we have from here to here so in real life what you're going to do is you would at the furnace right here you're gonna disconnect the white wire and the g wire and you're gonna wire nut them and then over at the thermostat you're gonna check from here green to your white wire and then you should have zero ohms unless one of the wires is bad so in this case our white wire is bad and so we're not getting our signal over to our terminal block in order to to turn our heat on so what we can do is see this little brown wire right here we can use that instead so we could switch the white wire out with this brown wire both here and over here and so that's what we would do on a surface call now that our thermostat wire has been replaced and our multimeter is set back on voltage for alternating current we're going to turn the power on and we're going to do our test again to find our problem [Music] so fan works heat doesn't work so now we're going to go ahead and test once again let's do our baseline from common to or our power so we have 28 volts and so if we're on heat then we can measure from common to w which is our weight wire and you see we have 28 volts so now let's go to the other side of the terminal block and now we can kind of jump along here we have 28 volts right there and we can file the wire over to over here so you can see we have zero volts right there so you can see that something just happened right now so it looks like a intermittent problem maybe a bad connection right here see we have 26 volts so it looks like a bad connection right there so the reason that our fan is turning on is because our sequencer temporarily had enough power to close the top contacts so let me just explain what's happening here this is a general purpose relay and it has 24 volts on the side here or it needs 24 volts on the side so we have a hot and a common in order to close these normally open contacts so they're normally open like this when you put power on the side over here they close so same thing here same thing here so basically for this light bulb to turn on this switch between this hot wire and this wire it needs to close and for this when these close it sends 24 volts over to the sequencer so then you have 24 volt power between here and here it heats the little disc on the bottom and it ends up pushing a rod and then what happens is these contacts up here they close and then they'll open up after a time increment after this little pain heater cools down at the base and so that's what's happening if you want to learn more you're going to have to look at the general purpose of relay video sequencer video fan relay video and contactor video which are all linked down in the description section below so what we found out is that we have a bad connection over here and so we need to go ahead and replace this wire or at least cut back and re-crimp this connector now that we've re-crimped our wire right here we're going to test out all of our functions and so turn the power back on and we test our fan first we'll test our heat second so our heat is working it looks like our general purpose relay if you heard that noise it may have suffered a little damage due to this bad connection right here so it would be a good idea to replace this general purpose relay so we do see that our our heat is working and now for air conditioning mode what i'm going to do is i'm going to take the face off and i'm just going to jump from r to y with my magnet jumpers and so these magnet jumpers won't work on these terminals but they will work on these i'm just waiting for my fan to shut off okay the fan is shut off now let's test from r to y for air conditioning mode so you can see our compressor is running meaning our light our fan is not running and so we know that our contactor must be sucked in and so it's allowing power across here so let's just we're going to measure our high uh voltage power so you can see 124 volts there we want to make sure that we don't have like a voltage drop or something like that we have 124 volts there in order to have that we would have to have our 24 volts across this uh contactor right here so we got our 28 volts remember anytime that a technician's talking about 24 volt power they're really talking about say 25 to 28 and a half or 29 and a half all right so that's done now we'll come over to our outlet we can get our screws but we want to make sure that not touch the uh the frame right here of the box so we see 124 volts on the sides of the duplex receptacle and let's just see right here 120 volts there so that's not a problem and as you can see we have our light lit we have 124 volts so we do have power to the fan so the fan must be a problem so what we're going to do is we're going to turn the power off we're going to switch our multimeter to electrical resistance and let's unplug the fan and then we're going to check our resistance and you see that we are reading ol which is open line you could also refer to that as open limit and so that fee and basically would be bad in this scenario so that's our problem so we would need to replace this so that you know the problem could be in the cord it could just be a burnt cord or something like that but in this case we're just saying that this is the fault so remember in an outdoor air conditioning system it's referred to as your outdoor condenser you're going to have a contactor there in order to turn on your compressor and your condenser fan so this represents the condenser fan this represents the compressor in this test i'm not going to bother putting the thermostat face on i'm just going to use my magnet jumpers so i'm going to first turn the power on and then i'm going to jump from r to g that turns the indoor fan on and it does that by putting 24 volts over on this side and then it allows this normally open switch to close and next i'm going to go from r to white and so you can see we have 24 volts over here and it's closing this switch allowing power to hear and closing this switch allowing 24 volts over to the sequencer pane it's heating up the pane and then after that this switch closes allowing the fan to turn on so that works and our fan is going to continue to run because of our sequencer sequence meaning time so it has a longer time for the delay off than it does for the delay on for this top section right here and then next what we're going to do is we're going to go from r to y and we heard our contactor click but we don't see our compressor or our fan running so which is our our light and our fan and so what we're going to do is we're going to come over here first and we're going to measure to see if we have 24 volts you see we are measuring 28 volts right here and we should because we have r to y so we should have 24 volt power here which you see that 24 volt power here and you can follow it over to that yellow wire on the side of the contactor and then you just move this probe over to the common so what i did before is i just kind of jumped right over to here and so we know we have power at the coil of the contactor and then we have a separate high power right here and just you know this is our connection point for all of our hots and all of our common neutrals and so this is a normally open switch and it's supposed to close when you have 24 volts on the coil so we have 120 volts there and let's see over here we've got nothing and so no volts and so that's a problem if we go from here to here you can see the difference is 124 volts that does not mean that this has power that means that this has power and this is at zero and the difference between them is 124 volts and so this switch is not closed so because of this we know that our contacts in here must be bad on our contactor and so this whole contactor ends up getting replaced now i just want to state this real quick and the statement really is that the 24 volt circuit is going to be separate from the high voltage circuit so that's true for our contactor for our fan relay for our sequencer and for this general purpose relay so the 24 volts right here is not in the same circuit it's not touching the high voltage one so i need you to know that this switch path is separate from this switch path so this switch path is controlled by the 24 volts on the pane heater pushing a rod so you're pushing contacts closed and open same thing here it's an electrical magnet it's 24 volts and the electrical magnet sucks the contacts together this is an electrical magnet as well when you apply 24 volts it closes the contacts right here so this this and this are electrical magnets this uses a base pane heater and a rod in order to open and close the contacts now that the contactor has been replaced what we're going to do is we're going to turn the power back on and we're going to use our mag jumpers we're going to go from r to g so that works let's go from or to w that works and let's just wait for our fan should be turning on soon if it is going to work and there it goes okay and then our last one is going to go from r to y and now we're going to go from r 2y so i don't know if you can see this hopefully you can but our little popper just tripped which is our 3 amp circuit breaker so typically you're going to have a fuse there and if that pops then you gotta trace down where the short is actually at and so let's go ahead and take these off first and in order to do that what we're gonna do is we're gonna change and go over to resistance and i don't know if you've noticed that but it only happened when we went from r to y which means that our problem is somewheres on our y circuit so we already know that and so it's not like we just turned the power on and the circuit breaker popped immediately it popped only during air conditioning mode and not even during the fan so with the power off we're going to pull our yellow wire out and now we could turn this back on but let's just once again just check this in the field we don't have a circuit breaker we have fuses and so we don't want fuse after fuses to fuse to pop we need to kind of cut cut the wiring in half and test until we find the direction which our problem is now let's also make sure we're jumpered again from r to y and i know the power is off right now we're reading the resistance of our transformer which is about two ohms so that's fine so we we're fine at two ohms now if we measure from here to ground we see we have a problem so you can see we're measuring 0.1 ohms so now we're going to disconnect from our contactor and so if we measure on the side of the contactor to ground we're probably going to be measuring the resistance value of the contactor but the contactor itself could be short of the ground in this case we're measuring 16.7 ohms so that's not the issue and we would have that same measurement even if we were to disconnect our common wires the whole point of why we were measuring to to ground was because of our common wire connections so if we measure from here to here you're going to see once again about 16.7 ohms so it seems that our wire is actually the problem so you can see we're measuring 0.1 ohms so it is just the the yellow wire so that one must have chafed along the frame right here so this is our ground frame and so it must be rubbing up against there and so that wire the yellow wire needs to be replaced we have our multimeter on voltage and we're going to turn our power back on and then we're going to use our magnet jumpers but before we even got to use these you see our little popper has tripped again so if this was a fuse that would mean it's a blown fuse so what we're going to need to do is we'll turn the power off and we're going to turn our multimeter to resistance and so because we didn't use these we know our problem is not on the w y or g circuits the problem is directly on the r circuit we know the problem is not on the common circuit because if we go from c to ground so let's just go right here you can see we have 0.2 ohms which is normal and so that's because of this wire right here so that's going directly to ground and so we know that that's not the issue our issue is with our r wire to ground and so you can see we have 0.1 ohms there so that is that is our issue now what we need to do is separate the r wire we're going to do that right here on the terminal block and so once again the power is off we can just go ahead and unscrew this right here and we're going to separate the thermostat and thermostat wiring from the basically the cabinet wiring so now we're going to go from here to here and you see we have no booms now once again we could go ahead and reset this and you see we have 1.2 ohms now that would be the same thing as if we went from right across this transformer from our to our common so we see that our transformer has a certain amount of resistance on that coil what we're looking for is 0.0 0.1 or maybe even 0.2 and so let's go from here to ground you can see 0.3.2 ohms so that's our problem right there is with our thermostat wire running from our thermostat to the terminal block so this r wire from here to here needs to be replaced we can do that with our extra wire which is actually our brown wire or just run a whole new thermostat wire so now we're going to turn the power back on and we're going to check everything with our magnet jumpers we're going to go from r to g so our fan works r to w so i hear the general purpose relay buzzing but i don't see the light right here and let's see if the the fan turns on for heating mode which it does so now we know we have 24 volts here because then that means we have 24 volt power coming over to here to power the base pane heater because we see the fan running but let's just take our measurements just in case we're getting an odd voltage so we're getting 27 volts there and so let's just make sure if we have our 120 volts from here to our common we have 124 volts there we have 124 volts there and so the next thing we'll do in this case what we're going to do is we're going to unscrew this bulb and we're going to measure inside so we have a little brass tab and then we have our side and so you can see we're measuring 17 volts so something's wrong internally inside this box because we see that we do have power here to our common so let's just check this for a sec so i'm going to keep this probe on our common this brass tab should be on the hot okay so that's 120 volts so it looks like our hot wire is intact and now let's go on this hot right here and to the common and see if that's the issue which now we see that that is the issue it seems to be our common wire is the problem because we are not measuring 120 volts now but when we measure from our hot inside the lamp to our common we do get 120 volts so we need to check out what's going on inside here and fix this so this is the problem right here this lamp holder i hope this video helped you understand how to troubleshoot using these eight scenarios on our electric board and if you want to learn how to make this board we have the full layout the step-by-step instructions the wiring diagram the measurements all over at acservicetech.com in the article section and the resource section also if you want to learn more about hvac you can take some some quizzes you can use some of our calculators you can read some of our articles and quick tips all over at ac surfacetech.com as well as our refrigerant charging and surface procedures for air conditioning book and so hope you enjoyed yourself and we'll see you next time at ac service tech channel

Channel: AC Service Tech LLC

Views: 177,971

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, thermostat, 24v, 24 volt, electrical troubleshooting, transformer, thermostat troubleshooting, contactor, general purpose relay, sequencer, fan relay, lil popper, multimeter troubleshooting, electrical diagnosis, hvac course

Id: xxclrVcvKSQ

Length: 26min 4sec (1564 seconds)

Published: Sat Feb 12 2022