Carrier furnace, model 58PAV111-20:
When the thermostat is bumped up to start the furnace, sometimes the inducer motor kicks in, will run for a few seconds, then stop. It may then kick in again after a minute or so only to stop again. Sometimes it will kick in and then the heating element will activate, and the furnace will continue in normal operating mode. This morning the inducer motor did not kick in at all when the thermostat was bumped up, so I ran the furnace through its test sequence. The first couple of times I tried that the inducer motor ran fine, the heating element came on, the hot air blower ran, and the cool down blower ran, as well. Afterwards I tried to get the furnace to run again, but the inducer motor never kicked in. The LED code showed "31", indicating the inducer motor or start capacitor (I don't believe this model even has one), or pressure switch may be at fault. So, I ran the test sequence again, and this time, and two additional tries afterward, the inducer motor did not run. Finally, this evening I gave the thermostat another try, and, to my amazement, the inducer motor immediately kicked in, did not falter, and the furnace actually ran normally through its cycle.
What are your thoughts on what is happening here? Obviously something is faulty in the system, but I am at a loss to troubleshoot the root of the problem.
Thank you for your assistance.

 

remove the stat off the subbase and jump R to W this will give you a constant heat signal till the jumper is removed(jump or unscrew one and screw it to the other)..with that the ID should constantly run also till the jump is removed.use the service switch on the furnace to cycle on and off...the ID runs and the Pressure switch sees the air pressure closes and the furnace starts spark...then main burner.if for any reason the ID stops the pressure switch opens and the burner drops out.is the squirrel cage centered up no rubbing?is the motor body hot to the touch after you see if not running but then it starts up?capacitor would be mounted right on the body..with the service switch off does the squirrel cage within the ID free spin either direction and or brake hard after spin.... every time your toggle up/ON the service switch.... the ID should start pressure proof and burner runs...with that original jump up on the stat

 

Thanks for the quick response.

Both the main blower squirrel fan and the inducer motor fan spin smoothly and without any rubbing or squealing. I haven't noticed whether the inducer motor body is hot to the touch.

I'll try out your suggestions the next time this furnace acts up (which could be as soon as this evening with this cold front coming through), and then give you an update. One thing I am assuming here is that ID is short for inducer motor. Correct?

Thanks again.

 

You have an ignition control module that is causing the problems and needs to be replaced. It's acting erratically now, but will surely fail completely before long.

Sminker is theorizing that the thermostat may not be switching on the inducer motor reliably. That's a useful theory to test. But the self test doesn't use the thermostat. Since the self test reveals that the inducer motor isn't turning on reliably, its pretty certain the the ignition control is failing.

 

Thanks, SeattlePioneer.
Any suggestions on how I might be able to test the ignition control module to make sure it's the culprit?

 

You've really already done that with the self test. The only reason for the erratic operation you describe in the self test is an unreliable ignition control.

 

Great, thanks again! If it were only Monday I 'd already have this taken care of.