Home › Air Conditioners › Parts › Compressor

Air Conditioner Compressor: What It Does and Signs It's Failing

The pump inside the outdoor unit (or in the back half of a window or portable unit) that moves refrigerant around the system. Most mini-splits use an inverter compressor that changes speed to match the load.

How it works

It squeezes low-pressure refrigerant vapor into hot, high-pressure gas and sends it to the condenser coil. The inverter board feeds it variable power so it can ramp up and down instead of cycling hard on and off.

Signs it is failing

• Outdoor fan runs but the air indoors isn't cold or warm
• Loud knocking, grinding or a heavy hum from the outdoor unit
• Breaker trips when the compressor tries to start
• Overcurrent, lock or discharge-temperature codes
• The unit shuts down repeatedly after a few minutes

Overcurrent, compressor lock, rotor position and high discharge temperature codes point toward the compressor, though manufacturers list low refrigerant, a closed service valve or a bad inverter board as common causes too.

Can you replace it yourself?

Your part: confirm the breaker is on, clear debris and snow from around the outdoor unit and clean the indoor filters, then reset power once. Compressor diagnosis means live high-voltage testing, and replacement opens the sealed system. Federal rules in the US say only an EPA Section 608-certified technician may open or recharge the refrigerant circuit.

Buying the right part

Compressors are matched to the system and refrigerant type. Ask the installer about warranty coverage before paying for a replacement, since compressor coverage often runs longer than coverage on other parts.

Error codes linked to the compressor

• E5Compressor overload or lock-up protectionDaikin
• E6Compressor won't startDaikin
• E8Compressor current too highDaikin
• H6Compressor position sensing errorDaikin
• L5Inverter output overcurrentDaikin
• E1Short cycling or a sensor fault, depending on modelFriedrich
• 65IPM (power module) protectionFujitsu
• 94Compressor overcurrent (trip detection)Fujitsu
• 95Compressor motor control errorFujitsu
• E5Over-current protectionGree
• H5Power module (IPM) protectionGree
• CH32 / CH33 / CH36Outdoor refrigerant or compressor protectionLG
• CH21 / CH23 / CH26 / CH29Outdoor compressor or drive circuit faultLG
• PC 00Inverter power module (IPM) protectionMidea
• PC 02Compressor or power module overheatingMidea
• PC 04Inverter compressor drive errorMidea
• PC 08Over-current protectionMidea
• U2Discharge temperature too high or low refrigerantMitsubishi Electric
• U6 / UP / UFCompressor overcurrentMitsubishi Electric
• E416Compressor running too hotSamsung
• E461 / E464Compressor or inverter faultSamsung

Last reviewed 2026-10-19.