Furnace/AC How to Troubleshoot The Control Board

hey guys J here with word of advice TV in the comment sections for some of my a/c fixing videos people have been asking me to make a video about how to troubleshoot a control board and they're actually really not that hard to troubleshoot unfortunately to troubleshoot a control board you do need a meter so if you don't have one you might need to get one so take your furnace doors off or your air handler and most air handlers or apprentices will have a control board some of the older ones will not for the most part there is a control board in every furnace typically it'll be located right in front of the blower housing where your blower motor is once in a while it'll be in the upper section too so the way it works is you got power coming in to the furnace or the air handler right here it goes into your power switch so if I turn that off it turns everything off then you see or the furnace so power goes into there the switch is on so then power goes into here line voltage and then from the junction box it goes down and the first place to stop set is the door switch as you can see mine is taped in order to check voltages you do have to have your door switch taped most furnaces will have a door switch either on the left or right or in my case in the middle so tape that or put a screw in it so it stays shut and then always keep in mind that it is live you have 120 volts somewhere there so be mindful and don't touch any terminals so you don't get shocked so after the power goes into the door switch if the door switch is closed the powered end goes into the control board typically it'll be marked line blind voltage goes into that terminal so from the door switch it goes into there and that's what powers up your control board so after power goes into it the circuit board part of it brings power to whatever is calling for power like the blower motor or the inducer igniter so what will happen is sometimes let's say during the AC season the AC outside will turn on everything seems to be working good but the blower motor inside of the furnace is not turning on sometimes what's wrong is that the board is not sending power to the blower motor and simply not powering it up or other times you have voltage coming in from the transformer 24 volts into the control board but then that voltage does not come back out that means there's some kind of a circuit or a diode or some of resistor inside the board that got burnt out so in a nutshell how I was taught is if there's power going in but no power coming out that means the board is bad so what I like to do when I start is I set my meter to voltage my door switch is taped shut so I have power going through I like to first verify that my furnace is getting power and a lot of times a good indicator will be the indicator light the diagnostic indicator light if that's blinking then most likely you do have power you have 120 volts and you have 24 volts but not all furnaces will have that light so what I like to do is check it quick so if you pull off the wire that goes to your line terminal from the door switch to our line terminal just pull that off stick one meter lead in there and with your other terminal you need to find a common somewhere I like to just use a the comment on the transformer just because it's more accessible than the rest of them and if you just stick your lead into the middle speed of that transformer common there you should get a hundred twenty volts so if you look at my meter you see 120 volts so from my line terminal to a common you're supposed to have 120 volts and I do have voltage there and that means my furnace is getting power and it's getting past that door switch so I can plug that back in next what I like to check is that my transformer is getting 120 volts as well so I'd like to loosen the connectors on the transformer black and white that's going to be your 120 volt side usually it's a black and white wire I like to just leave them like half on plug like that so I could put my meter leads on so you put one lead on the Colin from the transformer and one lead on the primary hot side and if you look at my meter you got 120 volts so the board is sending power to the transformer now if your board is getting powered if you check your line voltage on your line terminal and it's getting 120 volts but it's not sending power to your transformer so if you check the white and black on the transformer and there's no 120 volts then your board is bad and it's not sending power to that transformer next thing you want to check is the secondary side of your transformer so it transforms at 120 volts into 24 volts so if you go on this side usually I mean there are always different colors the secondary side lines the secondary side wires but they will be opposite of the 120 volts side if you put both of your leads on those you should have somewhere around 24 volts and there you go I have 28 volts so my transformer is sending 28 volts out and also there's a fuse in line with that sometimes it'll be on the board I don't have a place for it on the board so mine is placed in on the hot side coming from the transformer the 24 volt side and then what I'd like to do is track where those 24 Volt wires from the transformer go in my case it goes into the one side goes into the fuse my fuse is good goes out the other end and goes into the small X plug then the other wire right here the common also goes into the small X plug so the 24 volt wires go straight into the control ward sometimes they'll have their own terminals it'll be called secondary one and secondary two so if I put my meter leads into the molex plug a hot side and the common as you can see I have 28 volts going into the control board and after the 28 volts goes into the control board it will come out on the thermostat terminal strip which is right down here in mine it will look different on every furnace but for the most part it'll be in a row like this where it says WY RG c it for common so the next thing you want to check is R which is power to common or b or c sometimes do so if I check voltage between R and common as you can see on my meter I do have 28 volts so the board received 28 volts and it's putting out 28 volts at that terminal strip now if you're getting voltage that far then chances are your control board is good usually you're gonna lose voltage somewhere before that also what you can find helpful is on the back of your furnace door most of the time there will be a wiring schematic and it could be hard to follow like mine for example has a bunch of lines and stuff but if you look at just look on the schematic until you find the power supply which in my case is right here look for the black and white and then you can kind of follow those lines where they go into the board and I'll explain sometimes what color those wires are what terminals they go into and you know sometimes it will help you track down on the wires that way also if you do end up needing a new control board the way you go about looking for the new replacement board most of the time on the board itself it'll tell you it's model number or part number and in my case it even tells me replace with CNT to 184 so if I ever needed a new board all I had to do is look up this board right here and get it on Amazon or whatever and that is the basics of troubleshooting your control board sometimes it'll be some goofy situation and then it's not as easy to troubleshoot and you do kind of have to go case by case basis but for the most part if you follow that procedure you will be able to figure out if your board bet is bad or not so once again as a reminder if you have power going into it but it's not sending power out the board is bad same for a furnace for example if you have power going into it but it's not sending power to let's say your inducer motor or your igniter then your board is bad I hope that makes sense to you if you didn't quite get it you can ask me in the comments below and I'll try to explain it better down there and that is all I had for you today thank you so much for watching don't forget to match that like button on your way out and we'll see you next time [Music] you

Channel: Word of Advice TV

Views: 462,153

Rating: 4.8992572 out of 5

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Id: 52iq9rYI0mI

Length: 9min 10sec (550 seconds)

Published: Sat Jul 21 2018