Mid efficiency inducer fan will not start

jinxie · October 03, 2022, 09:45:45 AM

Good Morning

My mid efficient residential furnace will not fire up. Would someone be able to help me troubleshoot? I am mechanically inclined so I should be able to follow the necessary steps.
Here is what I know so far....
The furnace A/C works fine
When I switch the thermostat to heat or cycle the switc

h on the furnace you can hear and measure 24V power coming out of the transformer. You can also hear the relay on the circuit board "click" as power is turned on. (I assume that is what should turn on the inducer fan?)
No power at the inducer fan
I realize this is pretty vague, but it doesnt seem like there are alot of components in between to troubleshoot? For example there appears to be a pressure switch and the gas valve switch/wiring that probably controls the inducer somehow?

Admin · October 03, 2022, 09:51:16 AM

It sounds like a faulty control board that is not sending power to the inducer motor. You can wire the inducer motor to constant power to prove it works. It's usually pretty easy to connect the black inducer motor wire to the black line voltage wire coming into the furnace.

jinxie · October 15, 2022, 09:02:02 AM

Sorry for the late reply. Been very busy here
I had a chance to back probe 120v to the hot wire going to the inducer motor.
As soon as I turned the furnace motor on the fan started to run.
Should the furnace have fired up though because the sensors would have detected flow?
It still didnt fire up. So we confirmed the inducer motor works, but there is no power to the inducer from the original furnace circuit.
Everything else was connected. I just added power to the back side of the connector

Is there something else I can try? Rather than buying a new board immediately?
What else could be preventing power from reaching the inducer motor?
It looks like the power goes through the gas valve.....anything I can check there?

Thanks again

Porcupinepuffer · October 16, 2022, 07:23:25 AM

Have you confirmed from the board that pin 1 and 4 with the black and white don't give you 120v for the inducer during a call for heat?

I would also set up a small jumper between your thermostat connection point R and W right at the furnace. Just to make sure you're getting good contact for a call for heating.

jinxie · October 16, 2022, 11:51:28 AM

Test across the wires 1 and 4 coming from the 6 pin connector on the board? (P1)??

Porcupinepuffer · October 17, 2022, 04:09:36 PM

Quote from: jinxie on October 16, 2022, 11:51:28 AMTest across the wires 1 and 4 coming from the 6 pin connector on the board? (P1)??

yes

jinxie · October 20, 2022, 12:35:21 PM

OK 120V power comes out of the circuit board at #1 of the 6 pin connector and is 120V at the gas valve square block 4 pin connector at #2 pin. No 120V comes out any other pins. I would assume I should see 120V on #1 pin but there isnt 120v there.
So basically 120V isnt getting through the gas valve
What can I try next?
Thank you

Porcupinepuffer · October 21, 2022, 03:35:02 PM

Yes. Under a proper call for heat you would get the 120v coming off the gas valve from pin 1 of the c3 connector for the inducer. Do you also have the neutral working on pin 4 on those same connectors for both the board and at the gas valve?

I would also check to see if you have continuity between pins 1 and 5 on the c1 connection of the gas valve. Perhaps it's open and thinks it's unsafe to engage the inducer.