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ACiQ Single-zone wall mount, R-454B Error Codes
Older ACiQ (R-410A) units may show shorter codes. Refrigerant sensor codes (EHC/FHA) only appear on models with a leak sensor.
| Code | Meaning | What to check |
|---|---|---|
| EH 00 | Indoor EEPROM malfunction. | Indoor control board. |
| EH 0A | Indoor EEPROM parameter error. | Indoor control board. |
| EL 01 | Indoor/outdoor communication error. | Interconnect wiring, terminal screws, power at the outdoor unit. How to fix → |
| EH 02 | Zero-crossing signal detection error. | Supply power and indoor board. |
| EH 03 | Indoor fan speed out of control. | Indoor fan motor, blower wheel binding, connector. |
| EH 31 | Indoor DC fan motor voltage too low (units with a DC fan driver board). | |
| EH 32 | Indoor DC fan motor voltage too high (units with a DC fan driver board). | |
| EH 0b | Indoor main board and display board communication error. | Display board cable and connectors. |
| EH 60 | Indoor room temperature sensor (T1) error. | Measure the sensor; check the connector. How to fix → |
| EH 61 | Evaporator coil temperature sensor (T2) open or shorted. | Measure the sensor; check the connector. How to fix → |
| PH 0c | Indoor humidity sensor malfunction. | |
| EC 07 | Outdoor fan speed out of control. | Outdoor fan motor, obstruction, connector. |
| EC 51 | Outdoor EEPROM parameter error. | Outdoor control board. |
| EC 52 | Outdoor coil temperature sensor (T3) error. | Measure the sensor; check the connector. How to fix → |
| EC 53 | Outdoor ambient temperature sensor (T4) error. | Measure the sensor; check the connector. How to fix → |
| EC 54 | Compressor discharge temperature sensor (TP) error. | Measure the sensor; check the connector. How to fix → |
| EC 55 | Outdoor IPM module temperature sensor (TH) error. | How to fix → |
| EC 56 | Evaporator coil outlet sensor (T2B) open or shorted (multi-zone). | How to fix → |
| EL 0C | System low on refrigerant. | Leak search, starting at the flare connections. How to fix → |
| EH C1 | Refrigerant sensor detects a leak. | Ventilate, leak search; follow the A2L leak procedure. |
| EH C2 | Refrigerant sensor out of range and a leak is detected. | |
| EH C3 | Refrigerant sensor out of range. | |
| EC C1 | Another indoor unit's refrigerant sensor detected a leak (multi-zone). | |
| FH A2 | Communication error between the indoor unit and the refrigerant sensor. | Sensor cable and connector. |
| FH A3 | Refrigerant sensor internal error. | |
| FH A4 | Refrigerant sensor permanent error. | |
| FH A5 | Refrigerant sensor self-check failed. | |
| FH A6 | Refrigerant sensor low voltage error. | |
| FH CC | Refrigerant sensor error. | |
| FH 0P | Wireless module self-test failure. | |
| FL 09 | Indoor and outdoor units mismatched. | Confirm the indoor and outdoor model numbers are an approved match. |
| PC 00 | Outdoor IPM module protection. | Inverter board and compressor. How to fix → |
| PC 02 | Compressor top (or IPM) temperature protection. | Outdoor airflow, dirty coil, charge. How to fix → |
| PC 03 | Pressure protection (low or high pressure). | Charge, airflow, closed service valve, restriction. |
| PC 06 | Compressor discharge temperature protection. | Low charge or restriction is the usual cause. How to fix → |
| PC 08 | Outdoor current protection. | |
| PC 0A | Condenser high temperature protection. | Dirty outdoor coil, blocked airflow, outdoor fan. |
| PC 0F | PFC module protection. | |
| PC 0L | Outdoor low temperature protection (outdoor temperature below the operating range). | |
| PC 10 | Outdoor low AC voltage protection. | Supply voltage under load. How to fix → |
| PC 11 | Outdoor board DC bus high voltage protection. | How to fix → |
| PC 12 | Outdoor board DC bus low voltage protection. | How to fix → |
| PC 30 | System overpressure protection. | |
| PC 31 | System pressure too low protection. | How to fix → |
| PC 40 | Communication error between the outdoor main chip and the compressor drive chip. | How to fix → |
| PC 41 | Compressor current sampling circuit failure. | |
| PC 42 | Compressor start failure. | |
| PC 43 | Compressor lack-of-phase protection. | Compressor U/V/W wiring and terminals. |
| PC 44 | Outdoor zero-speed protection. | |
| PC 45 | Outdoor IR chip drive failure. | How to fix → |
| PC 46 | Compressor speed out of control. | |
| PC 49 | Compressor overcurrent failure. | How to fix → |
| PH 09 | Anti-cold-air in heating mode (normal at heating start-up; not a fault). | |
| PH 90 | Evaporator high temperature protection. | Dirty filter or indoor coil, indoor fan speed. |
| PH 91 | Evaporator low temperature protection. | Dirty filter, low indoor airflow, low charge. |
| - - | Indoor units calling for conflicting modes (multi-zone). Not a failure. |
How to read the codes
- EH = indoor, EC = outdoor, EL = communication or low refrigerant, PC = protection (compressor, inverter, voltage, pressure). LH/LC codes mean the unit is limiting its speed, not a failure on their own.
- To see stored codes, use the remote's information inquiry (service manual section 5.1). '- -' is a multi-zone mode conflict, not a failure.
- Power-cycle at the breaker for several minutes. If the code comes back, troubleshoot it.
Codes point to a circuit, not a part. Test before replacing boards or sensors. Inverter boards hold a dangerous charge after power-off; wait and verify DC bus voltage is gone before touching them. Refrigerant work requires EPA 608 certification.
Source: ACiQ Single-Zone Service Manual (6K–24K, R-454B), Error code of engineer mode, pp. TS 11–12. The "meaning" column follows the manufacturer's wording; "what to check" is our field summary. Always go by the label on the furnace you're working on.
Related
- Mini-split communication error troubleshooting
- Mini-split flare connections (the usual leak point)
- Look up any mini-split code
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