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I have a Goodman GMNT100-4 that air conditioner was working great. However, I recently turned on the heat. The system goes through all sequences fine until it's time for the blower motor to kick on, it doesn't. The system then shuts down because it's getting hot. I've replaced the blower motor and squirrel cage a few months ago. I've changed the primary limit switch, the lower one at the blower motor and the pressure switch. Is my circuit board bad? The only other thought is a bad rollover switch or something on the heat inducer... Any help will be greatly appreciated! Thanks!

  • Hello, and welcome to Stack Exchange. Was the furnace working after you replaced the blower? Have you tried measuring the voltage on the blower motor? – Daniel Griscom Oct 5 '18 at 21:48
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Check to see if the HEAT terminal on the circuit board is getting energized when the blower motor should be running. If the motor is getting power, but not spinning, then there's a problem with the motor. If the motor is not getting power, then there's a problem with the circuit board.

If the motor is getting power, but not spinning, it could be:

  • A bad connection between the circuit board and the motor
  • The wrong motor lead landed on the HEAT terminal (but that would likely just spin the motor at the wrong speed)
  • A bad motor capacitor (Probably not if A/C works)
  • A bad motor winding

If the board is not energizing the motor terminal, it could be:

  • A bad timer
  • A bad relay
  • A bad circuit board trace

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