Carrier furnace problems

Old 01-03-20, 01:56 PM
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Carrier furnace problems


First post here and I found already "Carrier furnace ECM blower motor problems". Very useful.

However, after troubleshooting everything I could think of, I'm at a loss: the furnace will work for some time then stop with code "12" or sometimes with "41". After power cycle, it usually restores normal operation for some time.

What I noticed, when in "self-test" mode (Sw1-6 ON) it runs through inducer motor low/high speed - always fine.
Blower low/high speed - low speed sometimes fails and then I get error code 44 twice, followed by 41.

Power cycle or retry - and it will do whole test without issues more often than not (got it to fail about 2-3 times out of around 10 tests).

For example, this morning error code 12 was blinking. I power cycled it and it's been working since. This scenario happened every day for the past several days.

What I have checked thus far:
- Self-test (using switches, SW1 - 6 to ON) failed with "12" or with 44 followed by 41, 2-3 times out of 10 attempts.
- Measured blower motor feedback voltage (seems to be within the spec)
- Disassembled blower motor ECM module; visual inspection - current inrush protector (thermistor) looks fine, measuring with ohm meter, resitance at room temperature 1 Ohm (conforms to the spec).
- Motor windings resistance - 4.7 ohm each phase, no conductivity to the housing (good).

Now, an observation in the failing case: when low heat is requested, it seems to be trying to spin up the blower. It jerks back/forth. This should be normal but after several attempts it fails to spin up.

It seems that high speed always works (at least I never saw it failing during a component test, SW1-6 ON).

Any suggestions on what could be causing it to fail to spin up at low speed?

For reference from:
Error code 12:
Blower Calibration Lockout: indicates RPM calculated for low heat was less than 250rpm or greater than 1300rpm on two successive attempts.
Error code 41:
Blower outside valid speed range - indicates the blower is not operating at the calculated RPM.

Ok, and as I went down to take a picture of the error code table, it went into "12" again. The sound from the furnace is a very short buzz (and I know while I was watching it fail the test it would do the same): it jerks the rotor a bit in one or the other direction and stops. It keeps trying several times, then stops.
Old 01-03-20, 06:20 PM
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12 is the code you get when you reset power.

BLOWER ON AFTER POWER UP (115 VAC or 24 VAC) Blower runs for 90 seconds, if unit is powered up during a call for heat (RW/W1 closed) or (R-W/W1 opens) during the blower on-delay period.
41 is a bad sign. It sounds like it may be time for a new motor.

If you are not tripping a door switch or flipping off and on the power switch You might inspect the field high voltage connections to the furnace ( with the power switched off).

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