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

The main board inside the indoor unit, behind the front panel or in the control box. It reads the room and coil sensors, runs the indoor fan and louvers, talks to the outdoor unit and drives the display. The EEPROM is a memory chip on this board.

How it works

The board takes your remote settings and sensor readings and decides what each part should do. It exchanges data with the outdoor board over the connecting cable.

Signs it is failing

• Indoor unit dead or display blank
• Memory (EEPROM) or display communication codes
• Remote signals ignored
• A stuck MANUAL/AUTO or keypad button code
• Codes that return right after a reset

EEPROM, display and some sensor and fan codes point to the indoor board. Many clear after a power reset of a few minutes.

Can you replace it yourself?

Turn the breaker off for a few minutes and back on. Check that buttons aren't stuck. Board replacement means working in the wired control box and sometimes reprogramming, so it's tech work.

Buying the right part

Indoor boards are specific to the model and capacity. Your installer or tech should order them.

Error codes linked to the indoor control board

• U4Indoor and outdoor units can't communicateDaikin
• UAIndoor and outdoor units don't matchDaikin
• A1Indoor unit control board faultDaikin
• A6Indoor fan motor faultDaikin
• C4Indoor coil temperature sensor faultDaikin
• C9Indoor room air temperature sensor faultDaikin
• E2Stuck button or a sensor fault, depending on modelFriedrich
• E3 / E4Frost probe open or shortedFriedrich
• E5 / E6Room temperature probe open or shortedFriedrich
• 11Indoor and outdoor units can't communicateFujitsu
• 12Wired remote controller communication errorFujitsu
• 18External or Wi-Fi adapter communication errorFujitsu
• 32Indoor unit control board errorFujitsu
• 35MANUAL AUTO button stuckFujitsu
• 41Room temperature sensor errorFujitsu
• 42Indoor coil temperature sensor errorFujitsu
• 51Indoor fan motor errorFujitsu
• H6Indoor fan airflow faultGree
• F1Indoor room temperature sensor faultGree
• F2Indoor coil sensor faultGree
• C5Jumper cap missing or wrongGree
• CH05Indoor and outdoor units aren't communicatingLG
• CH01 / CH02 / CH06Temperature sensor faultLG
• CH03Wired wall controller problemLG
• CH10Indoor fan motor problemLG
• EL 01Indoor and outdoor units have lost contactMidea
• EH 00Indoor board memory (EEPROM) faultMidea
• EH 60Room temperature sensor faultMidea
• EH 61Indoor coil sensor faultMidea
• EH 0bIndoor main board and display aren't talkingMidea
• E4Portable AC display panel communication faultMidea
• Blinking OPERATION lightWall unit's indicator light is flashingMitsubishi Electric
• P1Room air temperature sensor faultMitsubishi Electric
• P2 / P9Indoor coil temperature sensor faultMitsubishi Electric
• PbIndoor fan motor errorMitsubishi Electric
• FbIndoor control board errorMitsubishi Electric
• E0-E5Wall controller communication errorMitsubishi Electric
• E6 / E7 / E9Indoor and outdoor units aren't communicatingMitsubishi Electric
• E101Indoor and outdoor units aren't communicatingSamsung
• E121Room temperature sensor faultSamsung
• E122 / E123Indoor coil temperature sensor faultSamsung
• E154Indoor fan errorSamsung
• E162 / E163Control board memory errorSamsung

Last reviewed 2026-10-19.