Furnace/AC How to Troubleshoot The Control Board

what would be the problem if there is no voltage going into the door switch. a problem with the junction box? could be anything between breaker and door switch?

Thermostat Wiring Mistake - Furnace Dead, Need Advice

Accidentally wired thermostat “C” to “B” (brown) instead of “C” terminal. Furnace (Goodman) wiring was correct (Y/W/R/G/C). Ran fan overnight (no A/C). Next day, got 5 red flashes (rollout/fuse). Replaced fuse - furnace worked again.

Today, turned on heat - got a burning rubber/plastic smell, then shut it off. Now control board LED is dead, even with only R and W connected. Fuse looks fine.

Could the thermostat wiring have fried the board? Any safe DIY checks before I call for service (trying to avoid $150 inspection because I am broke)?

Do you think my bobos is bad because I get 24 volts from R to G, R to Y, R to C and R to W but when I go from Y to C I get nothing.?

I’m not getting voltage with y and c

We have a Ducane 92G1U and we’ve been trying to follow your videos and the board will power on and flash slowly but we can’t even get to the part of the sequence when inducer is suppose to turn on. We can viably see the blade not moving and we just had this furnace installed brand new exactly one year ago. We’ve tried testing the voltage and it does nothing on the meter or it either jumps around all over the place. Everyone just keeps saying replace the board. But we want to replace the inducer first.

I have the exact same control board. Have 120V to the transformer and obviously the 28.5V out of the transformer. 5A inline Fuse is good and I have 24V in and out of the board (actually, 28.5V) measured as shown in the video. But the control board LED is dark. Is the control board bad? or what should I test next? Call for heat?

Very through explanation. It helped me understand how to troubleshoot my board. Thanks for making this video.

That is where my filters must be, can't believe they put them inside that door.

Ok so ive got power to the shut off switch on the side of my furnace and the board is blinking 3 times when I turn the power on which indicates the uploader blower motor is bad is there some safety feature that causes no power to go to anything else thats supposed to have power like the electric gas regulator that turns on when the board tells it to open up so the furnce can start its fire up sequence? My blower itself turns on when i turn the A/C switch on that pushes the heated or cold air through the vent ducts but thats it . Ive checked for power at the inducer motor & theres no power to that either . The furnace is a American standard thats a high efficiency natural gas furnace thats been working great for years until 2 weeks ago when I noticed that it was getting cold in the house so i turned the heat up because it was 63 degrees in the house and the digital thermostat said it was in heat mode but it does nothing . I even checked the wires from the board back to the thermostat and did a continuity check & they both were good plus i changed the batteries in it thinking that maybe that was the problem at first . If i cut power to the furnce thats supposed to clear the codes on the board so i tried that a couple times but as soon as i turn the power back on that 3 blinking code comes on again so evidently the codes aren't being deleted & yes i taped that switch on the furnace like you showed but i mainly need to know if this uploader blower has some safety lockout feture so if it goes bad it shuts the power off to everything else except the board itself ?

I was able to jump my fan and furance from my control board. Is this confirmation that the board is good?

Your video gave me the basic knowledge to do enough troubleshooting to get my furnace running over a cold weekend without an expensive weekend HVAC visit. My low voltage fuse was blown and it happened when I switched the system to cool mode. It was very warm yesterday. It was the first time the unit had been switched on since last year. I suspect that I have an issue with the outside air conditioner unit - perhaps the contactor / relay switch. I will look further when it quits raining and isn't a weekend! As I like to say, unless they are hyper flexible, fuses usually don't blow themselves! Ha ha! Thanks so much!

Very helpful and informative.

I had no power to the draft inducer motor. The blower motor ran fine, but the board wouldn't send power to the inducer motor. I noticed there were 3 relays on the board beside the inducer motor where the wiring harness connects that activate power. Theres not much that can go wrong on a board other than an electrolitic capacitor or a relay. I ordered 3 new relays for 10 dollars and soldered them in. It runs perfectly now. A new board was hundreds of dollars online. Could try shaking the board a bit up and down and side to side and putting it back in to jostle the relay contacts, it might start working again if you're in a pinch.
I know in this day and age your supposed to just throw it out and buy a new one but I build and solder circuits as my hobby so felt comfortable working on the board.

My board has a blinking LED light and the fan turns on, but nothing else. Using the multimeter to the R and C, it barely registers and fluctuates, but nothing near what it should be. I'm not sure what the issue could be

Came home from work . Thermostat was set at 70 but house was at 76 . Turned off cooling/heating at thermostat and let it thaw out. ( suction line was frozen up to compressor) let it thaw out and turned it back on & everything outside at condenser was working . I even got cool air from the vents for about 10-15 mins . Then it stopped blowing . No air coming from vents. Went outside and it was frozen again ! Is that still a potential symptom of faulty control board ? Or more likely blower motor itself ?

Great video
Thanks for sharing
New subscriber here

Is the white-rodgers 50a51-495 a good replacement for Trane CNT03759 board? It's giving me intermittent shutdowns and sometimes "Replace Control" and sometimes "Thermal Protection Device Open". Furnace is Trane TDD060R936B0.

I have a 1194-200 control that has power and furnace turns on but it doesn't have 24VAC going to the outdoor unit.
Outdoor unit turns on when I manually push the contactor.
Could this be a bad control board or something else?

Unfortunately there’s a relay in the control board that is sticking so I need a new board

This channel has the best videos I have found for clear explanations and quality video of the tasks performed.

Ok Please help me with this. Lennox - Step 1-4 work fine. Calls for heat, inducer spins, limit switch fine, igniter lights.... then nothing for 4 tries... Watchguard error. I have a jumper from board to gas value that I use to light burner from igniter. Once burners fire, flame sensor stops igniter, and blower runs to heat the house... easy peasy.... WHY is the igniter not firing gas value??? it works just fine with jumper... runs like a champ with jumper no uses. 2 things to mention (Brand new board and new transformer installed)... Flustered beyond belief. All comments welcomed. Cheers

Hi J , what kind of power is that and where did you purchase your flashlight ? Thanks .

You can replace individual components on the board if your savvy enough. I do it on cars, Planes, etc.

Thank you so much for posting these videos. I has been watching them for 10 years. My Rheem gas furnace cannot pass the ingnior phase during the startup. 1) Pressure switch ok, 2) induce motor runs ok, 3) ignitor on, but 4) no gas came out from the gas valve. I measured the gas valve. There is no 24 V. The gas valve has two terminals with 2 wires (yellow and green gray). After a few tries, the control board sent flush code “1” (soft lockout mode). The yellow wire seems connected to a limit switch under the bottom of the blower. The control board has green light on. I measure 24 v from the transformer. I tried to get 24V directly from transformer, but it immediately shut off the ignitor. Is it a bad control board? Or any recommendations that I shall try?

has anyone ever saw only 76 volts coming out of the black terminal on the board, 138 volts on the red terminal, 98 volts on the blue terminal, 121 volts when i cross the blower motor commen terminal to door switch power? Not sure what the problem is but seams to be a bad board. on a Rudd 90+

Had the same company come 2 times, 3 different guys. They said you need a new unit. The heat works HOWEVER it will not come on in the morning at the scheduled time unless you turn the thermostat on and off. I have tried 3 different thermostats so I know its not the issue. During the day there are some times where it should kick on but will not unless we do a power reset. Any ideas? Gas forced hot air system about 12 years old.

Thank you

I checked everything and checked out good but my furnace still won't fire up why

Hey so my control board or PCB is faulty per the technician. If i replace it with the same exact control board/PCB....."Do i have to do any re-programming?" I can't seem to find this answer anywhere in google.

Hi there , my furnace is not working ,when I jumped R to W on the control board ,the furnace working back to normal , so what do you think it may be wrong?

Great video!

Hello captain Jay

I was getting voltage coming in to the transformer but 0 volts coming out . Checked r to c and got 0 volts. I replaced the transformer and still same issue . One of the terminals on the 24 volt side has power but the other terminal has no power . I’m assuming maybe something going on with the wiring? I checked all connections and everything seemed secure . Any ideas on what you might think it is? Possible circuit board failure ? There was LED lights on the board though .

I have a bad inducer relay. Can I just solder a new relay onto it instead of replacing the entire board?

love this one

Hey nice video but I have a question. My furnace turns on and then right back off within seconds. But if i take my test light and touch the white wire on the circuit board it's turns on and will run but if when I try to allow it to do it by itself it doesn't. I took out the rod and cleaned it but can't figure out what the problem is. If you can help i would really appreciate it. ( Help in Kansas ) City

Unbelievable Where can we ( all ) send you a few buck ? You deserve it. The time and money you save us ! And that's just for this first time, dealing with a repair. How about future situations ?! TY TY TY !

Just started doing service and ur videos r helping me out

that really helped thank you

Does all control board comes with a fuse i have honeywell ST9160B1027 i checked every step and theres power on the board but still heater won't turned on, blower works with the A/C but not with heat any suggestions? Thanks

I been trouble shooting my furnace for two years , my furnace would start heating but after a minute or two the blower would stop causing the limit switch to open if i don’t shut furnace off. i replace flame sensor and high limit sensor , issue continues. today I decided to take down my vivint element thermostat and i touched the R and W wires together and the furnace seems to be working had it run for 10 minutes and blower did not shut down . I was about to replace my board before i tried bypassing thermostat. i’ll do more testing to make sure that was it.

Have you ever heard of smart thermostat causing furnaces to am shut down mid cycle ?

My furnace has had a capacitor and the brain(board) go out along with the board again possibly, within just 3 months or less. Everything works now except for the heat. Had it tested and was told that only the "W" wire for the heat, was bad on the board but the rest of the terminals for AC and what not, worked fine. Was also then told that it could be because i didnt change the igniter and wiring harness using the retrofit kit i never got, when i changed the board. Even if i put a new board in, im being told that it will just burn out again without a new wire harness, old one is fine, and the igniter, which is brand new and i just replaced it. How would it be the wiring harness or igniter with the igniter checking out good. Igniter doesnt even heat up

Put a screw in it.....what😳

my unit has both the outside condenser/compressor and the fau fan working fine individually but the fan shuts off when I set the a/c to cool. Is this an indication the fan control board is at fault?

Thank you for the wonderful videos. I have an issue I am troubleshooting, if you can chime in. IFB sends 24v to the condenser every three minutes regardless of the indoor temperature reaching to the set temperature on the thermostat. Air handler and blower fan keeps running blowing warm air through vents after outdoor unit is off and until compressor engages again in three minutes. So the condenser fan and compressor are on for three minutes and off for three minutes. Subcooling on the unit checks out fine using liquid line pressure and temperature so not suspecting high or low pressure in the system. Contactor leads receive 24v every three minutes. I have checked the main and fan control board for damage or loose wires. This short cycling is not as bad but I think I have an issue I can figure out. Thank you in advance!

I have a board that isnt flashing at all. There is a 5 amp automotive fuse on it that blows as soon as you apply power to the unit. Could this be the board shorted?

My carrier infinity unit has frozen over once,tha thermostat is blank, plus all parts are New excepted my circuit broad outside it trys to start but does not what can I do for now,thank you for your help ( can't get rite).

Thank you for all your help❤❤❤❤

Please help. My control board passed all of your tests, but I'm not getting power to my ignitor. Do I need a new control board?