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Mitsubishi · Heat pump troubleshooting

Indoor fan does not run

What is going on

The indoor blower will not turn. The fan motor is a DC motor fed about 310-340 V DC from the indoor board.

Likely causes

  • Blown fuse on the indoor board
  • Drain pump shorted and taking out the fuse
  • No DC supply from the board
  • Loose fan motor connector CNMF
  • Faulty fan motor or indoor board

Check in this order

  1. Warning: High DC voltage on connector CNMF. Never unplug it with power on - it can damage the board and the motor.
  2. Check the fuse on the indoor board. If it blew, check the drain pump resistance before replacing the fuse; a shorted pump must be replaced.
  3. With CNMF unplugged and power on, measure pin 1(+) to 4(-): about 310-340 V DC, and pin 5(+) to 4(-): about 15 V DC. Missing = replace the indoor board.
  4. If the supply is good, check CNMF for poor contact. If the connector is good and the fan still will not run, replace the fan motor.

Applies to: PEAD-RP35/50/60/71/100/125/140JA and JA(L) ducted indoor units (220-240 V models)

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Source: Mitsubishi Electric PEAD-RP35-140JA(L) Service Manual, 10-8 DC fan motor check, p.39. Written in our own words; check the manual for your exact model.

For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.