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airheatman
airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8164
Experience:  Furnace, A/C and heat pump specialist.
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Changing out st9160 to st9120 furnace board, where do m1 and

Customer Question

changing out st9160 to st9120 furnace board
JA: Did you check the furnace's filters?
Customer: where do m1 and m2 as well as yellow and blue off transformer on blower fan connect to
JA: Do you plan on doing the work yourself?
Customer: I am in the middle of it
JA: Anything else we should know to help you best?
Customer: I have these four wire that were connected to old board 9160 not sure where on 9120 to plug into
Submitted: 9 months ago.
Category: HVAC
Expert:  airheatman replied 9 months ago.

I will be happy to help. Let me grab a manual

Expert:  airheatman replied 9 months ago.

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

Customer: replied 9 months ago.
The terminals are on what part of board
Expert:  airheatman replied 9 months ago.

Bottom left just below J! six pin plug

Expert:  airheatman replied 9 months ago.

If you have further questions, please let me know.

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Customer: replied 9 months ago.
Yellow to c or X
Blue to X or c
Not sure
Expert:  airheatman replied 9 months ago.

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

Customer: replied 9 months ago.
Furnace still is not starting
Expert:  airheatman replied 9 months ago.

Do you have a volt meter so we can troubleshoot? And do you have door switch held in ?

Customer: replied 9 months ago.
I sent the phone request in make it quicker and easier does it go to you?
Customer: replied 9 months ago.
I have a volt meter ready
Customer: replied 9 months ago.
Says phone call not available
Ok
Expert:  airheatman replied 9 months ago.

Start by checking 120 volts into transformer and 24 volts out.

Customer: replied 9 months ago.
Still there
Customer: replied 9 months ago.
Sorry need more coaching
White and black test board power on?
Unplug yellow and blue at board?
Expert:  airheatman replied 9 months ago.

See below check for 120 in and 24v out of transformer

Customer: replied 9 months ago.
Power on red to L1 black to black on six pin shows nothing
Customer: replied 9 months ago.
Main switch is on
I hear humming
Customer: replied 9 months ago.
Status light is flashing on board
Customer: replied 9 months ago.
Led on gas valve unit is flashing too
Expert:  airheatman replied 9 months ago.

See the drawing I made, Check between white Neutral and Black L1

Customer: replied 9 months ago.
On V with solid bar nothing
On V with wave bar 35
On yellow blue
Expert:  airheatman replied 9 months ago.

Not sure what you are referring to.L1 and Neutral are on control board

Expert:  airheatman replied 9 months ago.

OK I understand you are referring to the meter. The V with squiggly bar is correct

Expert:  airheatman replied 9 months ago.

Tell me black to white on L1 and N and tell me between yellow and blue at C and X

Customer: replied 9 months ago.
I put red meter tip on black wire on L1 then black meter tip on black within 6 pin the black wire is coming from the transformer no reading present to check for power from board to tansformer
Customer: replied 9 months ago.
Really appreciate the help told (wrongly) this is a a plug and play replace the board
Expert:  airheatman replied 9 months ago.

Black meter lead needs to go to L1 on board, not 6 pin

Customer: replied 9 months ago.
Sorry meter set at 200 put black on L1 and red on neutral white wire reading is 157
Expert:  airheatman replied 9 months ago.

That is high. How about between C and X?

Customer: replied 9 months ago.
Is at 35
Expert:  airheatman replied 9 months ago.

OK you have an electrical issue.WE can not have over 127 in and 28 out. Check a nearby recetcle or in breaker panel

Customer: replied 9 months ago.
The furnace is on its own dedicated breaker still moved it to an empty new breaker same readings
Expert:  airheatman replied 9 months ago.

How about other outlets in the house see if they read that high

Customer: replied 9 months ago.
Just tried a couple yes same ...
Meter of out of calibration
Expert:  airheatman replied 9 months ago.

Either meter is out of calibration or high voltage is the problem. Board can not handle 157 volts

Customer: replied 9 months ago.
Must be meter (between 10-15 years old )
If it was that bad would have lost electronics by now
What else to check for,
Expert:  airheatman replied 9 months ago.

IK next with door button held in touch th R and G wire on board together and see if blower will start

Customer: replied 9 months ago.
worked
Expert:  airheatman replied 9 months ago.

OK tell me about the valve What is furnace model and valve number and what is the light doing

Customer: replied 9 months ago.
Furnace is a keep rite
Model n8mpno75b12a1
Manufactured Aug 2004
By international comfortHoney well valve says replace only with model sv 95541
Green led flashing on off 30 seconds with a hum
Then turns off flashing error codeGreen led flashing
Customer: replied 9 months ago.
Have left thermostat on calling for heat
Error code I'd 3 flashes the pause
Customer: replied 9 months ago.
Inducer fan not turning on when humming either
Expert:  airheatman replied 9 months ago.

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

Expert:  airheatman replied 9 months ago.
Customer: replied 9 months ago.
No power on volts going through black & white wires to inducer fan
Also tried a continuity test with both terminals got zero just like crossing pins on the meter
Expert:  airheatman replied 9 months ago.

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

Customer: replied 9 months ago.
Blew and ducked on hose can hear valve inside clicking
Checked for power from gas valve (two blue) power there
Customer: replied 9 months ago.
What should I check next
Expert:  airheatman replied 9 months ago.

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.

Customer: replied 9 months ago.
When ducking zero on ohm meter
When not get one on ohm meter
Expert:  airheatman replied 9 months ago.

OK now do same with wires connected. but just make sure the switch is open.It will not close unless inducer starts

Customer: replied 9 months ago.
Did the same sucking with wire connected
Ohm meter almost got to zero ran out of ability to suck any more in
Expert:  airheatman replied 9 months ago.

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.

Customer: replied 9 months ago.
What's next sir
Expert:  airheatman replied 9 months ago.

That is about as far as I know to go without actually being there. I can open to other experts if you would like

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