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.