Is the relay REALLY bad? | Understanding HVAC Electrical Concepts

today's video is going to be a very simple video it's going to be on relays and contactors and what i'm going to try to get across to a few of you is the way that i would check a relay i recently had an issue with a blower motor not working and some people that i were around they were like hey it's it's it's a new motor so nobody ever used their meter to troubleshoot they just assumed that because the motor wasn't turning that the motor was the problem and of course it wasn't and then the capacitor got replaced and then the thermostat got replaced and and there was a lot of assumptions so today what i'm going to get across to you is what i would do and how i would do it as far as checking and troubleshooting for a in this instance for a blower motor not working so uh let's look at uh some some real quick items on a relay and remind you about a few things and then we'll look at a trane air handler that i have behind the camera it's a tem model and it has a it doesn't have a board in it like a goodman it just has a fan relay so we'll walk through this shouldn't be too long of a video but uh some some very crucial basic information and it seems that people have forgotten it so uh let's turn to it and we'll get started all right so i got a couple components here a relay of contactor i've got a meter and we're going to start real simple so what is a contactor and a relay if you remember what you've learned about contactors and relays if you've been through any training course or or in the field long enough right it's this is a two-part component and a contactor is real easy to see you can identify where the 24 volt coil is and this is more so residential stuff right there are contactors that have 120 volt coils or a 208 240 coil or even a 460 in in some you know rooftop package units on the commercial side but speaking just for like residential stuff a real simple contactor is generally generally 24 volts and that coil is controlled by the thermostat and it may or may not have some low pressure switches or high pressure switches or some type of safety wired in series with that circuit but generally on a contactor the y circuit ultimately ends at the contactor coil and when that coil gets powered it energizes right and it's going to cause this switch to react okay and like i said it's real simple this is a one pole contactor it's only a switch in one side depending on which way you hold it it's still left or the right you know no big deal but uh it is a big deal you should replace it just like it it's in there but don't forget that this is a two-part component the coil and the switch the switch shouldn't open or close until the coil does something you know to cause that reaction so the thermostat controls the coil the coil controls the switch and then the switch turns on the motors or turns off the motors so too easy while a contactor is is pretty much a normally open switch or switch is relays tend to mess with people so this is uh this is not the 9340 relay that i like it's a real simple relay that's in this train air handler that we're going to look at but it follows pretty much the same setup and if you look at the side all right it gives you a very simple excuse me there we go it gives you a simple depiction of what the internals look like so terminals one to three is going to be you can see a little squiggly line that's going to be your coil and you'll just look here and find terminals one two three and then it tells you terminals two to four it's open and terminals five to six is closed so it identifies that two to four is a normally open switch and five to six is a normally closed switch it's identical in its function to the 9340 relay that that a lot of people have done some stuff on and i've done you know my share of talking about it so if you had to look right people get all nervous when you start adding wires to it and stuff but if you were to take this thing apart come on there we go uh if you were to take the top off of this one uh you can't do that with the 93 40 is pretty much riveted in or whatever but this little black pilot duty relay uh you'll you'll see a coil here and then you'll see your switches okay relays are a little bit different than contactors they still follow the same premise right you got to get power to the coil in order for the switches to move and react to that and with a relay since this is going to be a fan relay you'll probably generally see the the two to four in this case the normally open switch that's going to be used to power the fan for cooling or for fan only operation and then we'll probably use the normally closed switch to tie into our heat sequencer so that when the heat strips come on we can send power from that high voltage heater circuit through the normally closed to get our fan to come on with the heat strip so typical stuff nothing fancy coil at the bottom this coil is going to be energized by the thermostat and it's it's going to be tied into the the g circuit the indoor fan relay circuit so once this coil gets powered down here on terminals one and three then two and four will close and five and six will open too easy what i think people are are confusing themselves on is is they're not remembering that there's two two parts to this now if either part is bad then you get a whole new you know a whole new relay so if you go to a contactor and you say oh the coil is shorted we don't replace just the coil anymore that's not made that way so you'll just get a whole new contactor or if uh in the case of the contactor the the switches burn up maybe you had uh you know some some arcing or the pitted contacts on it if this if the switch is messed up and the coil is fine either way you still replace the whole contactor uh the fan relay is going to be the same thing doesn't matter if the coil is shorted out or open or if the switches are burn up or something either part goes bad you replace the hole all right but you have to know how to troubleshoot this all right so the switch is a switch switches switches are in line with one leg of power coils they are a load so they're going to get they're going to see both sides of power but you have to remember that the load is different than that switch i can check these individually the low voltage coil and then the high voltage switches we can do those individually and still troubleshoot properly so let me uh let me take you over here to the air handler and we're going to look at it and i'll show you how i would troubleshoot it and might even go ahead and do one on the contactor coil or the contactor itself on the outside portion of this unit okay so hang tight and we'll uh we'll look at the air handler all right so i've got my meter stuck up in the corner and i'm going to try to keep it close enough for you to see and far enough out the way at the same time all right so i've got power onto the air handler and here is my fan relay like i said no circuit board in this particular case and i'm going to walk you through the same problem that i've heard about recently so this fan motor is not working and the first thing you need to understand is the sequence of operation is that the thermostat calls for the fan to work okay so if the thermostat was doing his job and i'm not going to bore you to death with continuity checks and stuff like that i mean you know they're coming if you uh depending on the problem that you got but if my fans not working the first step i would do since you've got the cover off to the air handler is take your meter and go from the g terminal on the on the relay to the common and i've got zero volts all right now once i you know prove power or something like that and you can even check 24 volts out the transformer secondary if you want but as far as i'm concerned right now this relay is not turning on the fan because it hasn't been told by the thermostat now i'm going to reach up here and turn the thermostat on so i just turned on the the fan from auto to on and what i'll do i think there's a slight delay in the in the thermostat right so what i'm doing now is i'll do the same check on the coil and you can see i've got 26 volts so from the common to the coil uh the g to the c right is 26 volts that means that coil is getting power from the thermostat now let's say that and i'm going to take this off real quick let's say that i got 24 volts on the relay coil but my fan still didn't work the next step i would do is still low voltage related i would leave everything powered on and this is me i'm going to take the green off okay so no 24 hot and what i'm going to do is i'm going to ohm out or use continuity rather either one i mean they're both related and i'm going to just because you have 24 volts going to the coil terminals [Music] doesn't mean you got a good coil you could have an open coil and that 24 volts is not going to do anything so while you're there checking 24 volts on those two terminals go ahead and real quick take one of those wires off and on out the coil so i did the continuity and you can hear it beeping if you just switch it to ohms right i'm going to get the same thing 78 79 ohms for me personally ohm values are are in my head i make it real simple if i see ol like you do here on the screen right now right let me turn that up there [Applause] if you see ol on a on your uh when you own out a coil then what that means is this there's nothing there worth anything between these two leads ol is a bad reading if you see zero which is what you get when you basically put the two leads together that means there's no resistance there so you basically go from from both you know both far ends of the spectrum either all the resistance in the world being ol or no resistance both of those are bad what i need and and john doesn't know every you know on value out there but what i know i need is some positive number between 0 and infinity and then i've got got a starting point in my mind i can say you know what that's something like a load at least the voltage has something to work with and go from there so once i've confirmed that i've got 24 volts to the coil and that i actually have a coil there to work with now we're going to get into the switch part of things so what i would do then is i would go back to volts on my meter all right let me pan you back i would go to volts on my meter and i'm going to check my air handler voltage and i've got 208 in this case now if you've seen any video i've done like the high voltage hopscotch and even hopscotch with with the the low voltage or whatever this is my terminal block this is my power it's a good source and i'm always going to reference here i think what messes a lot of guys up about switches is until you're mentally ready for it as a technician you can check you know any terminal you want your meters just going to tell you the difference in the voltage but if you don't know what to expect then this hopscotch thing is probably the best way to do this so what i'm going to do is i know that on a relay since the switch breaks one side of power um on this fan really not not a two-pole contactor but on this fan relay specifically i know that i'm going to have l1 coming in and that switch is going to break that contact and l1 is going to eventually go out to turn it on turn the fan motor on so i'm going to keep one lead on l2 and i'm going to reference l1 right and you can see here i've got my 208 power source my total voltage a lot of guys they dig in me on this right but but i know i've seen i'm seeing my total voltage so i know that i've got power sitting at that relay i also know that l1 is only half that voltage l2 is the other half right but but work with me i've got power going into that relay and if i check that was terminal 2 on the the normally open switch which it should be closed now that i've got power for g if i check the other side and i've got the same 208 then that means that power went into the switch and then back out if you were to check power in and then when you checked it coming out you get zero that means that that switch has not passed that power okay power going in and not coming out that's a bad switch okay so i don't know how it is in in your particular setup but if you will reference the terminal block and find out l1 and l2 you can leave one lead there and follow power in and out of those switches and when it goes in and don't come out you know that might be part of your problem so but in this case i've got the power on another way you could do this is if you were to take the wires off right don't a lot of guys are going to get me on this right i have disconnected the high voltage completely from this relay alright let me move you so you can see it i took the high voltage off completely now this is a live circuit so i'm sure somebody out there is going to mess with me right but you can hold this out the way and the coil is separate than the switches so if you had to you could easily do continuity on the normally closed and say hey it's open now that's only half the check the real check would be uh if you remove power on the low voltage did it go back closed and it did so that's good now since i've got power off the coil i'm going to ohm out the open side and it's open no beep i got a beep when i touch my leads i got no beep when i do the switch if i were to reapply coil voltage that switch should close so and it did so i mean there's a couple ways you could do it with if you're familiar with the voltage on the switch or if you have to use voltage reference to the terminal block however you do it but know that the thermostat controls the coil if there's a good coil there then that coil is going to control the normally open and normally closed switch in this case some relays only have one or the other or some release for some relays have both or multiple sets of both so make sure that the thermostat controls the coil the call controls the switch and in this case once the switch passes power out we've got a psc motor in our unit here so if you have a psc motor and the motor is not working and you've verified low voltage to the coil you verified voltage in and out of the relay switch you may want to check your capacitor and then the motor so but a lot of people here lately have been blaming relays or capacitors or bad motors without troubleshooting and this is just a a snapshot of troubleshooting it so i hope it makes a little sense to you there's a couple guys that i'm trying to get this across to really and i know that they'll probably watch this so let me go check a contact and i'll be the last thing and then we'll be done now one thing i'll tell you too is if you have voltage to the coil then the thermostat's not the problem if you don't have any voltage here on your 24 volt connections to that coil then don't blame the relay yet you need to troubleshoot and find out where your 24 volts went in this case on the g circuit but if it's a contactor you would make sure that if you don't have 24 volts on the contactor coil then you would of course need to maybe troubleshoot low pressure switches or a float switch or something of that nature but if voltage is there then we're going to all mount the coil if needed if it's not there then we're going to backtrack in the wiring and find out where the voltage went all right so here we are on the outdoor unit for the air handler we just left and what i'm gonna do uh is keep the meter kind of off screen i'm gonna check the bottom here i got no power so um if you're working with a psc motor like a compressor that has the contactor and the capacitor and everything outside i mean that's that's typical stuff but um the side of the contactor in this case is pretty cool you know pretty much color coded the the y is here and your common is on the other side so it's the side terminals but like i said in the case of a contactor this is pretty much a normally open switch this particular train unit has a single pole contactor so if i'm getting if i'm coming out here and i've got you know the the outdoor unit's not running one of the first checks i'm going to do is to the side of the contactor and i've got in this case 0 volts so what that means is the low voltage hasn't energized that coil yet so i would then backtrack maybe to the wire nut connections for the defrost board uh or further back all right if you have 24 volts to the side of this contactor energizing the coil and the switch here isn't pulling in then the easiest thing to do since you're right here is to pop off one of the leads on the side switch your meter over to ohms or continuity and check the side of that coil for a resistance reading in this case i get 14.4 so i can safely say in my head that hey if this coil were to get powered then it should move the switch a lot of guys are going out here and they're pushing their finger on the contactor switch that's not the way this is intended to work so use your meter if you if you have 24 volts then the next thing i want to do is remove the low voltage wire on on at least one side and on out the coil you may not have a good coil there you can have the voltage but if there's not a load if there's not a coil there to use that power then it's not going to move that switch so if you do have 24 volts there and you have a good coil and the switch isn't moving then maybe there's something internal broken you're probably not going to see that but that's when we would go and we could do some voltage checks or if you wanted to you could remove the uh the power off the bottom and do continuity through it you know something like that you can treat it very much the same as a relay it's just that to understand that this this contactor only has you know a normally open switch it's not like a relay where it's got or can have uh you know a different uh setup as far as normally open normally closed switches said but that's what i would do check the sides if i don't if i if i have power there then i'm going to all mount the coil and then proceed with the troubleshooting steps if i do not have 24 volts then you have to remember that the thermostat sends power to the coil then the coil is going to energize and move the switch then the switch is going to have to pass power that your high voltage power to whatever motor compressor outdoor fan indoor fan you know whatever you have even heat strips i mean the principle is still the same so make sure you have your voltage from the thermostat and the outdoor units like i said the only thing i would really be worried about is if you have like a refrigerant leak then your low pressure switch might be open but you would backtrack from here to find out where your voltage stopped it's it's going to be some type of switch more than likely so but anyway i hope that makes a little bit of sense i'm just trying to refresh a couple people's mind to make sure that you're troubleshooting as as best you can uh if we were going to guess at everything we wouldn't buy all these tools so the tools are what you need to master you need to get the basics down in your head and don't let something as simple as a bad relay or a bad contactor cause you to misdiagnose and then possibly you know get to get looked at funny by a customer when you tell them hey this is a you know a bad you know 500 motor or whatever and it's really just a simple you know hundred dollar contactor so troubleshoot it as best you can do it right if you have any questions then let me know until next time one other thing i'll tell you is if you ever think that the fan motor is bad um the last little cheap trick i could tell you is to use something like this uh spade clip uh one guy that i know he calls this a bunny clip b-u-n-n-y like a bunny rabbit because it's got like two ears on it and it's uh some guys call it a splitter i'm not sure the exact uh nomenclature of it what i usually do is take a real simple piece of wire with two male connections on it and if you ever think that the relay is bad and you want to check the motor you can easily put this little jumper in here and see if the motor starts working you're essentially straight wiring the the high voltage circuit for the motor to make sure that the motor is getting the proper power in my case here my terminal block does not have any male connection points that i could use so this jumper wire would be great for me if you did have some uh or a unit with a terminal block that did have those you could easily just take this and plug it straight on to the power of the terminal block so um so that's about it hopefully you understand a little bit about the relays on the contactors between diagnosing the thermostat properly and knowing how to troubleshoot it a little bit and diagnosing a relay making sure that you check the coil and the switches separately and together you'll get a little bit better at properly diagnosing bad motors bad capacitors you know bad relays and bad thermostats so until next time i'm out of here

Channel: John Jennings

Views: 57,798

Keywords: HVAC Troubleshooting, HVAC Electrical, HVAC Electrical Troubleshooting, high voltage hopscotch, Fan Relay, Goodman Board, low voltage troubleshooting, low voltage hopscotch, low voltage problems, hvac low voltage, hvac fan not turning on, hvac fan relay, fan relay continuity, fan relay coil, fan relay ohms, fan relay checks, hvac fan not turning off

Id: wYz894L3mLI

Length: 24min 58sec (1498 seconds)

Published: Wed May 25 2022