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Old 05-08-2008, 11:23 PM   #1
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Inducer fan assembly or inducer control circuit board failing


I've got a 20 year old Carrier furnace, and the inducer fan was intermittently failing. Sometimes the fan would come on and the pilot would light, and sometimes it wouldn't. Eventually the fan failed to come on at all.
I'm trying to figure out whether it is the fan, or the circuit board with the contact breaker points on it, that needs to be replaced, or both.
Which of the following 2 statements does anyone think makes the most sense.
1. "the inducer control is bad which probably caused the inducer motor to fail due to improper voltage and amps"
2. "The failing/failed fan motor assembly more than likely caused an over amperage concern on the circuit board, heating up a relay and causing an intermittent failure of the circuit board. This won't be detected until you replace the failed fan motor with a new one"

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Old 05-10-2008, 09:01 PM   #2
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Inducer fan assembly or inducer control circuit board failing


Generally speaking, a motor either works or it doesn't.

Intermittent problems are usually either the controlling device, in this case the relay on the board, or wire splices/connectors.

Here's how I would go about troubleshooting this; first, get the system to call for the inducer fan to run. Next, check for voltage across the motor leads. Most likely 120AC, but could be 24AC. If there's voltage across the motor, but it doesn't run, then the motor is bad.

If no voltage across the motor, look for voltage across the relay contacts. If there's voltage across the relay contacts, then it's not conducting. Look for voltage across the relay coil. If you have coil voltage (usually 24AC), and voltage across the contacts, then the relay is bad.

Look for voltage across fuses. If you have voltage across a fuse, it's blown.

These are basic tests, there are alot more if needed.

Rob

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Old 05-11-2008, 07:17 PM   #3
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Inducer fan assembly or inducer control circuit board failing


Hi Rob,
Thanks for your suggestions. It looks like the relay contacts (points?) are very pitted. I'm thinking that may be why it's gradually been failing.
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Old 05-12-2008, 08:28 PM   #4
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Inducer fan assembly or inducer control circuit board failing


There's a good chance that pitted relay contacts will fail intermittently with a small motor. Not enough current to keep them clean. If you can catch it while it's failed and measure voltage across the contacts, or even wiggle them a bit with a screwdriver (careful, they're live!), you'll know for sure.

Rob
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