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Carrier · Heat pump troubleshooting

Outdoor ECM fan not running - Carrier 25HNB9/24ANB1

What is going on

Compressor runs but the variable-speed outdoor fan stays off.

Likely causes

  • No 230 V to the motor
  • No PWM signal from the board
  • Loose motor connections
  • Failed motor

Check in this order

  1. Confirm 230 V is present at the motor (power on, unit need not run).
  2. With the motor unplugged, read DC volts across PWM1 and PWM2 against the PWM table.
  3. No signal check board connections, then replace the board.
  4. Signal present reconnect the motor and recheck; if the signal drops or the motor ignores it, check connections then replace the motor.
  5. Bench check with PWM wires off the board, 24 VAC on the PWM leads should run the motor at full speed.

Applies to: 25HNB9, 24ANB1

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Source: Carrier Residential AC & HP Application Guideline and Service Manual 24-25-9SM (text export), ECM Fan Motor Troubleshooting. 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.