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Old 05-02-2011, 06:32 PM   #1
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No heat from furnace

I have a Goodman GMH950904CXAB furnace. When call for heat the circulation blower runs but no flame. LED is on control modules(normal operation) checked fuse, ok. I checked both rollouts, primary limit, and aux limit switches...all normally closed. The draft induction motor does not turn on. I checked resistance on the draft induction motor and got around 2 ohms. I checked the control board W and C for 24v and got nothing. I checked for 120v at the draft induction motor and got nothing. what do you think? bad control?


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Old 05-02-2011, 06:51 PM   #2
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You need to have 24 volts from W to C when it is calling for heat. If not your tstat is kaput or you got broken wiring. Remove and label the tstat wires on the board. Then put a jumper between R and W and press door switch in carefully. If it works then you have the aforementioned problems. You had the power On and door switch pressed in when you were trying this did you?


"Cut it twice and it is still too short".

Last edited by yuri; 05-02-2011 at 06:53 PM.
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Old 05-03-2011, 04:20 PM   #3
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Thanks Yuri,

I had no volts at w and c so I jumpered between r and w and everything fired up normally. My next step is to jumper r and w at tstat to verify if my wiring or tstat is bad.
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Old 05-04-2011, 11:23 AM   #4
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with the stat off the subbase you should have 24V between R and C that is a constant...jumping R to W and the heat runs tells you the stat is the problem not the run up(stat wires) from the furnace
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Old 05-04-2011, 01:03 PM   #5
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No Heat from furnace

You stated that the induction motor is not coming on. Is this happening when the unit is all buttoned up? This should be the first thing that you here, when you call for heat. If the blower is the only thing that is running it may have gone out of start/run/shut down cycle due to a power outage or a short cycling from someone playing with the thermostat. Make sure the unit is closed up and ready to run, then unplug the unit at the wall and wait a short time - about a minute - then plug it back in. Also, if you have had any electrical work done lately make sure that the phasing is correct at this plug. The boards are very sensative to incorrect phasing and will not work properly, if at all!
Now go to the thermostat, which should have been off and go into the heat mode in auto, and then set the temp you desire then leave it alone!!
If it is a cycling problem, the control board should have cleared itself and the unit should work properly. Let it run thru a full cycle satisfying the temp set on the thermostat and shut down by itself. If you do not hear the induction motor come on, unplug the unit (always) and if you can try hand spinning the induction motor to see if it is free spinning or not. If it is stuck or slugish, use a little lite lube to see it that helps. Important - the induction motor is part of a safety system that makes sure that your exhaust venting is clear to the outside. This keeps exhaust gases out of your supply air and your household safe. Even if the motor begins to turn - it must turn at a designed RPM so as to properly operate the - vaccum safety switch - which should be connected to the induction housing via some sort of tubing. If the switch is not properly activated, the gas valve will not open and the air supply blower may be the only thing that comes on. This does this to clear what the unit has designated as run or failure.
Hope this helps, if not, get a well trained professonal to check it out.
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