Need - Suspect Gas Furnace Inducer Motor Problems

Problems related to residential installations.

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Need - Suspect Gas Furnace Inducer Motor Problems

Post by frnc5cmuntea » Sat Dec 08, 2012 11:46 am

I have a 373LAV (Horizonatal) Bryant Model Gas Furance (about twelve yrs old). The furnace works intermittenly, but usually doesn't work. I am getting a 31 code, meaning "Pressure, Draft Safeguard, or aux limit switch did not close or reopened."

What I noticed is that when the thermostat calls for heat, the inducer motor starts to spin, but trips prior to reaching full speed, and thereby stopping the furnace startup sequence. Sometimes (rarely) the inducer motor will reach full speed, which allows the startup sequence to continue to flames. But usually, the inducer motor trips prior to reaching full speed.

I have replaced the pressure switch and draft safeguard limit switch. I do no supect the furnace vent exhaust duct piping to be plugged, because when the unit trips, the limit switch does not need to be reset and it also trips with this limit switch jumpered. In addition, the flue stack has a well designed cap on the roof that would make it extremely diffcult for anything to get in.

I have also run the self component test on the unit and the igniter and blower seem to function fine, but again the inducer motor does not run to full speed and trips pretty quickly.

I suspect the inducer motor is going bad...though I am not sure how to check it. I don't want to replace the inducer motor unless I will be doing so with some favorable confidence that it is indeed bad. Any thoughts on how I can check the inducer motor or does the inducer motor have a start capacitor that might be bad as well

Appreciate any help please.

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- Need - Suspect Gas Furnace Inducer Motor Problems

Post by Freon » Sat Dec 15, 2012 11:20 am

What exactly do you mean the inducer "trips"? Are you saying the pressure switch is shutting down the ignition process because the inducer is not able to satisfy the needed pressure? TEMPORARILY jumpering the pressure switch will tell you if you're not getting the correct inducer pressure.

If that's the case, remove the inducer and see if the blower wheel is in good condition. Wiggle the shaft and see if there's play. The bearings may be going bad. You could probably oil the bearings and at least get the motor to temporarily attain the needed speed.

I doubt there's a run capacitor on that small motor. If there was, it would be very visibly mounted.

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