Blower runs constantly but draft inducer will not turn on

Anonymous's Avatar (by Gravatar) by Anonymous in  Climate Control » Heating 

I have a 25 year old Carrier furnace. The first problem I had was the burners lighting then after a few seconds turning off, followed by a relight and so on. I changed the pilot/flame detector. The furnace then didn't work at all...not even the draft inducer. I put a screw driver in the fan (outside) and pulled it through like a prop start on an airplane, the motor turned on and the furnace ran again for 24 hours. The draft inducer motor was obviously bad and I changed it out. Now the blower runs constantly, and though the draft inducer has 120 vac going to it, it will not turn on. I tested the motor and its good. I changed out the inducer control board, and did a continuity test on the pressure switch and the limit switch (both good) but no change. Any ideas?

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Answer by homeowners

There's 120V coming to it and it won't turn? This does sound like the draft inducer problem, probably in its wiring hookup. I am assuming you've checked that the fan can actually turn by itself (with power off) - i.e. not a mechanical problem like a bad bearing or something like that.
Is this an OEM replacement motor like Fasco for example? The color of the wires may not be exactly the same as on the original motor. Is this a shaded-pole or a PSC (permanent split capacitor) motor? I've attached FACO typical wiring diagrams, see if you can verify that the colors and the functions of the wires correspond. Shaded-pole with only two wires is kind of hard to mess up, but PSC, especially multispeed - it's possible. 

Answer by

Thanks for getting back to me. The old inducer wouldn't turn smoothly so I bought a replacement motor kit and new blower wheel. I tested the new inducer (while installed) by attaching a jumper from one of the motor connectors to ground and it worked perfectly (also turned in the correct direction). It's only a two wire motor with both wires the same color. It's strange that the inducer won't run and the main blower won't turn off. I changed out the ancient thermostat with a new digital one last night but it didn't help.

Answer by homeowners

When  you say

by attaching a jumper from one of the motor connectors to ground and it worked perfectly
- do you mean you did it while there was a call for heat from the thermostat and the main blower was working?  Does the control board require a Hall effect sensor on the inducer? It's the feedback that tells the controller that the inducer does turn and lets controller calculate the RPMs. Have you installed it?

Can you put the old one back in and see if it's able to drive the inducer? 

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