I have a Carrier WeatherMaker 9200 Furnace - Model # 58MXA100-16. The Draft Inducer Motor works intermittently. When heat is called for, the Draft Inducer Motor will always attempt to start. Sometimes it continues and the furnace will run normal as was the case for approximately 6 consecutive days last week. However, this past week, there have been numerous instances when the Draft Inducer Motor will NOT continue to run , thus prohibiting the furnace from igniting and ultimately producing heat. The times that the Draft Inducer Motor does not continue to run, the control board displays a “31” Fault Code. According to the manual, this Fault Code implies that the Pressure Switch will not close or reopen. I’ve verified the following:
1) Pressure Switch ~ 25.5 VAC.
2) Condensate Trap cleaned & OK.
3) Inlet/Outlet vent pipes are OK.
4) 115 VAC to Draft Inducer Motor when actually running.
The manual also states that the Motor Start Capacitor may be bad.
Questions:
1) Has anyone experienced this type of behavior with a Carrier WeatherMaker 9200 Furnace?
2) Where is the Motor Start Capacitor located – on the control board?
3) Could the control board be defective?

Thank you in advance.

 

I'd use a jumper wire to connect the R and W terminals, which eliminates the thermostat and should keep the inducer motor running. Or you can use a multimeter to verify that the 24 VAC remains steady at W when the inducer motor shuts off.

If W is energized the inducer motor should run and stay running. If it's not, most like the circuit board or ignition control needs to be replaced.

A bad capacitor would prevent the inducer motor from starting but not shut it off once it running, so that's unlike to be the problem.

 

Thank you SeattlePioneer for your suggestions. An update – I measured the “W” terminal and I indeed get ~26 VAC regardless of whether the Inducer Motor is running or after it attempts to run and fails to continue. This would imply that the T-Stat is OK. Therefore, it is most likely the control circuit board? Whenever the T-Stat calls for heat and the Inducer Motor attempts to run but fails to continue to run, I can cycle the “ON/OFF” power switch several times (clearing the “fault”) and finally get the furnace to run. Does this bit of information / behavior suggest anything else?

 

may be a bad bearing in inducer motor...next time you catch it not working feel if the motor is hot or try to spin it counter clockwise by the plastic cooling fan

 

Deans suggestion is a good one.

You KNOW the inducer motor should stay running. Now the question is identifying where the defect is that causes the inducer motor to stop.


When it quits, I'd check to see if you have 120VAC being supplied to the inducer motor by the circuit board. If you do and the inducer motor stops, you know you have a bad inducer motor.

If you have, say, 85 VAC or 0 VAC, you have a bad circuit board.

Turning the fan wheel to see if it's stiff because of failed bearing or if it's overheating and shutting off on a thermal limit switch are additional checks you can do on the inducer motor. But I'd check the voltage too.

It's a good practice to use several different ways to confirm and verify a problem if they are available.

 

Thanks guys for your suggestions. I had already verified that there was NO voltage to the inducer motor when it would stop even though heat was still being called for.

Follow-up: I delayed posting an update for being afraid it might jinx me. Anyhow, on Tuesday - 28 Dec 2010, I removed the control board and inspected it and found qty 2 power resistors (R33 & R34) had "cold" solder joints. I re-flowed these solder joints and then re-installed the control board and the furnace has not hiccupped since (knock-on-wood).

Again, I'd like to say "Thank You" for your help/suggestions.

 

mjgork,

Thanks for posting your detailed "fix". My furnace problem presented with similar symptoms. My unit would fail to heat almost every time the thermostat called for heat. The majority of time that the furnace was asked to heat, the inducer motor would either start, then immediately shut down or simply not start at all. It would generate the "31" LED error code. I have 2 identical furnaces, so was able to swap pressure switch, start capacitor before I found the post about testing input voltage to the motor. I tested the input voltage and found the 120V would show at the inducer motor, then drop off to zero(motor would start then stop) or be at zero (motor would not start at all). I pulled out my control board and found resistors R33 & R34 showing evidence of high heat and possibly cold solder joints as well. I too re-flowed and replaced the board. After multiple cycles, my unit has worked flawlessly.

 

Folks, a big thank you for everyone here ! This thread literally saved me 800$ (the cost some local company quoted me to replace the control board, they recommend potentially changing the draft motor for another 800$ too).
I have the same model of furnace with the exact same symptom. Luckily i have a HVAC friend who pinpointed out this thread, so I sent him the control board (1000 miles away) and he remade the solders around the slightly smoked (R33, R34) capacitors, everything works fine now.