29 y/o Carrier Gas Furnace Stpped Working

[Dr_Zoidberg57]

Carrier Gas Furnace, Model# 396GAW000075ACAA


This morning awoke to no heat. All was working fine the day previously. Checked thermostat and it appears okay. Checked all the breakers and they are all fine. The circuit board was replaced just 4 years ago. I opened the top part of the furnace and checked to make sure the fan was free spinning and it was (my neighbor had their motor seize up last year). When I pushed on the door power switch, I can hear the relay on the circuit board clicking. The blower motor sometimes makes noises like it’s trying to start, the fan will spin very slowly and then stop. Other times, nothing happens. In either case, all I hear is a low buzzing noise coming from the motor.

If it is the motor, where might I be able to find a suitable replacement? Do I have to pull it out to get the appropriate part number?

Thank you very much.

 

[user 4883]

To be sure, check for correct voltage to the blower motor.
If your lucky, it is nothing more than a bad capacitor.
you will have to pull the blower assembly to get the specs for both the motor and capacitor.
it is hard to get exact motor replacements but, graingers would be a good start to find one.

 

[Dr_Zoidberg57]

Thank you for the reply. I'm going to pull the motor tomorrow. We're lucky to have a Graingers less than a couple miles away. That's were our neighbors got theirs from.

 

[Dr_Zoidberg57]

I'm assuming, which is not always the best thing to do, the the voltage going to the motor should be 115V and not fluctuating between 20.0 and 0.00 volts? Also after unplugging the motor from the circuit board leads, the buzzing/humming noise seems to be coming from a small transformer just below the circuit control board. It's never made that noise before. I checked it's output and it 25 volts, which is what it says it should be on the schematic (115 to 24 volts). I'm guessing that if it's putting out the correct voltage that it's also getting the correct voltage coming in. So does that leaves the board itself?

This motor does not have a separate capacitor.

Thank you very much again for the suggestion to check the voltage to the motor.

 

[Dr_Zoidberg57]

Well, decided it was time to call in an expert. Turned out to be a bad pilot switch.

Appreciate the help. Sometimes it pays to know when you're in over your head.