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Discussion Starter #1
Just started this week. Furnace will work very intermittently.

When I turn it on either it will work or I can hear the smaller blower motor running but the big motor will not turn on. Also heard some sharp crackling noises (more on this shortly)

Things I have done - took the upper & lower cover. Checked to see if the reset button was tripped - was not. Reinstalled the lower cover and then manually held in the safety switch. The big blower turned on immediately and after reinstalling the cover (thus closing the safety switch) the blower works okay. The air temp from the vents is cool however. Sometimes it will start blowing warm air just fine. Will heat just fine then the temp starts dropping again and if you listen to the furnace you can hear the smaller motor running and seems like the furnace is trying to ignite.

Do not see any issues with water contamination although it has been raining pretty hard. However if it was a water issue blocking the vent I would suspect i would never kick in.

I read that there are some self diagnostic you can do on the circuit board and also see a label showing how to initiate it. Should I try this first?

Also this is equipped with an electronic air cleaner. When I held the safety switch in I could see arcing from the romex cable to the furnace housing. Turning off the electronic air cleaner (has a shut off switch) and arcing goes away. not sure if we are dealing with a bad heater or just shorted wiring.

Thank you for any ideas and suggestions. With work being very slow spending a lot of money on this is simply not in the Winter budget at this time.
 

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If the blower panel has a window in it, that is to look at the flashing error code. look at it before removing panels or turning power off next time it stops working. then look at legend to see what the code means.
 

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Roofmaster
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You must have your fan switch set to ON on the thermostat instead of Auto if the blower comes on as soon as you close the interlock switch. Did you kill the power at the breaker for 1/2 hour go back and turn on power, then try thermostat to call for heat? Get on cell phone to helper, Turn power on in breaker, have helper turn up stat while you look through observation port of burners, and record what happens, sounds and all. Inducer (little) fan should cut in for a while, then igniter should glow, then you should hear a click, which is solenoid on gas valve. pilot gas should flow and ignite, then burners cut in. In a little while big fan should spin up to blow heat through ductwork. Record what happens then come back.
 

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The control board brings the fan on when power is applied and it is also getting 24 volts to W. Blower runs for 90 seconds, its programmed into the control board.
 

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Update

Okay found an awesome event list on the order of startup.

1- Turn on heater
2- Inducer Blower kicks in - verified blower is turning on
3- Contact inside pressure switch close - not sure how to verify this but am assuming this happening as the next steps work.
4- Can verify ignitor getting red after 10 or so seconds burner lights (the one under pilot)
5- Verify 24 volts at gas valve

I also ran the self test on the circuit board and it appeared to turn on everything as it should with the self test
Meanwhile 2 more things to report.

There was a cannister with a larger clear plastic tube that went to a plastic housing with another smaller hose coming from the inducer blower housing into it. The line was full of water - took off the hose and found the cannister plugged with debris. Cleaned it out and drained all the water I could find. Did not help but I am assuming this is the water drain from condensation?

Also when the furnace was trying to start i lightly tapped on the gas valve and it turned on. Ever since that the furnace has worked.
Gas valve time?
Thanks
 

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