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Air Conditioner Outdoor control and inverter board: What It Does and Signs It's Failing

The electronics in the outdoor unit, sometimes on one board and sometimes split in two. The control side runs the outdoor fan, valves and sensors; the inverter side, with its IPM power module bolted to a finned heat sink, converts incoming power to drive the compressor at variable speed.

How it works

Power comes in, gets converted to DC and then rebuilt into a variable-frequency output for the compressor. A heat sink sensor watches the module temperature and the board shuts down if it overheats.

Signs it is failing

• The outdoor unit is dead but the indoor unit has power
• IPM, inverter or heat-sink overheating codes
• Overcurrent or voltage codes
• The unit runs briefly and stops
• Burned smell from the outdoor unit

Inverter, IPM, heat sink, voltage and overcurrent codes all touch these boards. Supply voltage problems, a blocked outdoor fan or a failing compressor cause the same codes.

Can you replace it yourself?

Shut the breaker off for 5 to 10 minutes, then clear the outdoor coil and fan. Inverter boards can hold a dangerous charge for several minutes after the power is cut, so diagnosis and replacement are for an HVAC technician. Some faults here end up as refrigerant repairs, and those need an EPA Section 608-certified technician in the US.

Buying the right part

Boards are matched to the outdoor unit model and sometimes need settings or jumpers moved from the old one. Leave sourcing to the tech.

Error codes linked to the outdoor control and inverter board

• U4Indoor and outdoor units can't communicateDaikin
• U2Power supply voltage problemDaikin
• UAIndoor and outdoor units don't matchDaikin
• E1Outdoor unit control board faultDaikin
• E5Compressor overload or lock-up protectionDaikin
• E6Compressor won't startDaikin
• E7Outdoor fan motor faultDaikin
• E8Compressor current too highDaikin
• F3Compressor discharge temperature too highDaikin
• F6High pressure in cooling modeDaikin
• H6Compressor position sensing errorDaikin
• L4Inverter heat sink overheatingDaikin
• L5Inverter output overcurrentDaikin
• 11Indoor and outdoor units can't communicateFujitsu
• 62Outdoor unit main board errorFujitsu
• 63Inverter errorFujitsu
• 65IPM (power module) protectionFujitsu
• 94Compressor overcurrent (trip detection)Fujitsu
• 95Compressor motor control errorFujitsu
• 97Outdoor fan motor errorFujitsu
• 99Reversing (4-way) valve errorFujitsu
• E6Indoor and outdoor units can't communicateGree
• E5Over-current protectionGree
• L3Outdoor fan airflow faultGree
• F3Outdoor air temperature sensor faultGree
• F4Outdoor coil sensor faultGree
• F5Compressor discharge sensor faultGree
• H5Power module (IPM) protectionGree
• CH05Indoor and outdoor units aren't communicatingLG
• CH67Outdoor fan blocked or faultyLG
• CH32 / CH33 / CH36Outdoor refrigerant or compressor protectionLG
• CH21 / CH23 / CH26 / CH29Outdoor compressor or drive circuit faultLG
• CH93Outdoor unit not powered or not respondingLG
• EL 01Indoor and outdoor units have lost contactMidea
• EH 00Indoor board memory (EEPROM) faultMidea
• EC 07Outdoor fan speed out of controlMidea
• EC 53Outdoor air temperature sensor faultMidea
• EC 52Outdoor coil sensor faultMidea
• EC 54Compressor discharge sensor faultMidea
• PC 00Inverter power module (IPM) protectionMidea
• PC 01Supply voltage too high or too lowMidea
• PC 02Compressor or power module overheatingMidea
• PC 04Inverter compressor drive errorMidea
• Blinking OPERATION lightWall unit's indicator light is flashingMitsubishi Electric
• E6 / E7 / E9Indoor and outdoor units aren't communicatingMitsubishi Electric
• U3 / U4Outdoor temperature sensor faultMitsubishi Electric
• U6 / UP / UFCompressor overcurrentMitsubishi Electric
• U8Outdoor fan stoppedMitsubishi Electric
• U9 / UHPower supply or current sensor problemMitsubishi Electric
• E101Indoor and outdoor units aren't communicatingSamsung
• E458Outdoor fan errorSamsung
• E221 / E231 / E251Outdoor temperature sensor faultSamsung
• E461 / E464Compressor or inverter faultSamsung
• E466Power supply voltage problemSamsung

Last reviewed 2026-10-19.