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Carrier · Air conditioner troubleshooting

Compressor will not run - winding and electrical checks - Carrier split systems

What is going on

Compressor does not start, hums, or trips on internal protection.

Likely causes

  • Internal overload open (hot compressor)
  • Open, shorted or grounded winding
  • Bad run/start capacitor or PTC
  • Low voltage
  • Locked rotor

Check in this order

  1. Let a hot compressor cool so the internal line break can reset.
  2. Power off, discharge capacitors, remove C, S, R leads.
  3. Find terminals largest reading is S-R, the remaining terminal is C; C-S is the higher of the other two.
  4. An open reading on any pair means an open winding - replace.
  5. Check to ground with a megger or high ohms scale; low reading means grounded - replace.
  6. Check capacitors; replace any bulged or leaking one. PTC start thermistor 12.5-ohm type should read 12.5-22.5 ohms.
  7. If the compressor draws locked-rotor amps with all external causes cleared, replace it and check the system for the root cause.

Applies to: Carrier/Bryant split AC and HP

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