Induction fan running constantly
#1
11-16-10, 09:47 AM
Induction fan running constantly
I have a Trane combination heater/AC, about 15 years old. Last week the heat would not come on and I had a tech look at it. He said the induction fan motor had burned out (which was consistent with the burning plastic smell my wife reported the last time the heat worked) and quoted me an outrageous replacement price. I picked up one myself and put it on and when I powered the unit up, the fan runs continuously, whether the thermostat is calling for heat or not. In fact, if the thermostat calls for heat there is no ignition and the board flashes a code for a pressure problem. If I unplug one motor lead from the board, power the unit up, and (carefully) plug the lead back in to start the fan, the unit ignites fine. I'm guessing the pressure switch senses a "zero" pressure when the unit is first powered on, and a continually running fan won't provide a differential it can sense?
Anyway, is it likely that the real problem is the board is bad and basically ran the old motor to death without me noticing? If so, is there a relay that I can remove and replace (I have moderate soldering skills) or do I just need to swap the board out? And is the latter something that a somewhat handy individual can attempt on their own?
Alternatively, did the tech put the unit into some kind of diagnostic mode (or his own ad hoc version) to test the induction fan motor and just leave it in that state assuming he would do the repair? I didn't see anything obvious, but I'm not entirely sure what to look for.
Thanks for any info you folks can provide.
Anyway, is it likely that the real problem is the board is bad and basically ran the old motor to death without me noticing? If so, is there a relay that I can remove and replace (I have moderate soldering skills) or do I just need to swap the board out? And is the latter something that a somewhat handy individual can attempt on their own?
Alternatively, did the tech put the unit into some kind of diagnostic mode (or his own ad hoc version) to test the induction fan motor and just leave it in that state assuming he would do the repair? I didn't see anything obvious, but I'm not entirely sure what to look for.
Thanks for any info you folks can provide.
#2
11-16-10, 10:23 AM
Banned. Rule And/Or Policy Violation
The sequence of events that should happen is:
1) the thermostat calls for heat
2) the inducer motor switches on and comes up to speed
3) the pressure switch senses adequate negative pressure to operate the furnace safely and turns on the hot surface ignitor, which glows white hot
4) the main burner gas turns on and lights off the HSI
5) the fan starts and circulates air around the house.
From your description, it's likely that the pressure switch isn't closing. You should use an AC voltmeter to check to see if it's closing or not.
Since you replace the inducer motor, I'd be concerned that you didn't get the right part. Did you get the factory replacement part specified for the furnace?
Please describe how you got the part.
1) the thermostat calls for heat
2) the inducer motor switches on and comes up to speed
3) the pressure switch senses adequate negative pressure to operate the furnace safely and turns on the hot surface ignitor, which glows white hot
4) the main burner gas turns on and lights off the HSI
5) the fan starts and circulates air around the house.
From your description, it's likely that the pressure switch isn't closing. You should use an AC voltmeter to check to see if it's closing or not.
Since you replace the inducer motor, I'd be concerned that you didn't get the right part. Did you get the factory replacement part specified for the furnace?
Please describe how you got the part.
#3
11-16-10, 10:48 AM
The fan motor I purchased is identical to what I took off (had to replace the original a few years ago due to a rusted impeller) and the part number checks out.
The problem in that sequence you posted is that the motor is on as soon as I flip the breaker and does not shut off no matter what other errors occur or what the thermostat is calling for. I think the pressure switch is fine, since I can manually simulate what the board should be doing by plugging the motor lead in after the unit powers on and calls for heat, whereupon ignition happens just fine. After the thermostat discontinues the call for heat, of course, the inducer fan does not shut off, though.
The problem in that sequence you posted is that the motor is on as soon as I flip the breaker and does not shut off no matter what other errors occur or what the thermostat is calling for. I think the pressure switch is fine, since I can manually simulate what the board should be doing by plugging the motor lead in after the unit powers on and calls for heat, whereupon ignition happens just fine. After the thermostat discontinues the call for heat, of course, the inducer fan does not shut off, though.
#4
11-16-10, 10:57 AM
Banned. Rule And/Or Policy Violation
Yes, it sounds like a bad circuit board probably damaged when being overloaded by the failing inducer motor.
So you got a "twofer," one bad part damaging another.
The short answer is that nothing should cause the inducer motor to run if the thermostat isn't calling for heat. Since it is, the part turning on the motor is bad, which is the circuit board.
That would be my conclusion.
There is no diagnostic mode the repairman could have left on inadvertently.
So you got a "twofer," one bad part damaging another.
The short answer is that nothing should cause the inducer motor to run if the thermostat isn't calling for heat. Since it is, the part turning on the motor is bad, which is the circuit board.
That would be my conclusion.
There is no diagnostic mode the repairman could have left on inadvertently.
#6
11-18-10, 08:19 AM
Actually, I'm having a little trouble making sure which board I need to order for a Trane YCC030F1M0BC and whether I need an additional kit if the original board has never been replaced.
#7
11-18-10, 08:45 AM
Banned. Rule And/Or Policy Violation
Sorry, I can't help you.
I'd call a Trane distributor with the model and serial number of the equipment and they can help you if they want to do so. Trane distributors don't have a reputation of being helpful to DIYers, but give it a try.
I'd call a Trane distributor with the model and serial number of the equipment and they can help you if they want to do so. Trane distributors don't have a reputation of being helpful to DIYers, but give it a try.
