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I will be happy to help. Let me grab a manual
M1 and M2 are unused on the 9120. They can be taped off, They are unused motor speeds.
The yellow and blue that went to 24VAC will go to X and COM to C
Bottom left just below J! six pin plug
If you have further questions, please let me know.
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Normally blue is C, If you do not remember give me model on furnace and I will see if I have a diagram if there is not one on furnace
Do you have a volt meter so we can troubleshoot? And do you have door switch held in ?
Start by checking 120 volts into transformer and 24 volts out.
See below check for 120 in and 24v out of transformer
See the drawing I made, Check between white Neutral and Black L1
Not sure what you are referring to.L1 and Neutral are on control board
OK I understand you are referring to the meter. The V with squiggly bar is correct
Tell me black to white on L1 and N and tell me between yellow and blue at C and X
Black meter lead needs to go to L1 on board, not 6 pin
That is high. How about between C and X?
OK you have an electrical issue.WE can not have over 127 in and 28 out. Check a nearby recetcle or in breaker panel
How about other outlets in the house see if they read that high
Either meter is out of calibration or high voltage is the problem. Board can not handle 157 volts
IK next with door button held in touch th R and G wire on board together and see if blower will start
OK tell me about the valve What is furnace model and valve number and what is the light doing
OK the 3 flash erorr is an open pressure switch because inducer is not coming on to close it. Next check for 120v to inducer fan on call for heat
Tap on pressure switch,The remove hose from inducer and suck and blow on hose to see if switch is opening and closing.Then retry
Unplug wires to pressure switch , suck on hose to switch and check continuity across switch.Make sue it has no continuity when not sucking on hose and we get continuity when sucking.
OK now do same with wires connected. but just make sure the switch is open.It will not close unless inducer starts
OK not sure why but the board is not sending signal to the fan. Since the pressure switch is open the board should send 120 to fan as soon as you call for heat.
That is about as far as I know to go without actually being there. I can open to other experts if you would like