Mitsubishi Heavy Aircon Error Codes and Blinking Light Patterns Explained

Mitsubishi Heavy Industries (MHI) air conditioning systems are known for robust engineering and commercial-grade reliability. When an MHI system encounters an operating anomaly, it displays alphanumeric error codes on wired controllers or blinks the **RUN** (green) and **TIMER** (yellow) LEDs on wireless indoor units. Understanding MHI error codes allows Singapore homeowners and property managers to quickly identify system conditions and take appropriate action. ## MHI LED Blink Pattern Diagnostic Matrix For MHI split units using LED indicators, count the number of flashes on the RUN and TIMER LEDs between 2-second dark pauses: * **RUN LED Flashes Continuously / TIMER LED 1 Flash:** Indoor room temperature thermistor open/short circuit (Code E6). * **RUN LED 1 Flash / TIMER LED 2 Flashes:** Indoor heat exchanger thermistor resistance fault (Code E7). * **RUN LED Flashes Continuously / TIMER LED 6 Flashes:** Indoor fan motor speed feedback anomaly (Code E9/E19). * **RUN LED Keeps Flashing / TIMER LED Keeps Flashing:** Serial communication signal line failure between indoor and outdoor PCBs (Code E5). ## Key Mitsubishi Heavy Alphanumeric Error Codes When using wired remote controllers (e.g., RC-EX3 or RC-E5), specific codes appear on the screen: * **E1:** Circuit board communication error or remote controller signal loss. * **E5:** Communication error between indoor unit and outdoor condenser. * **E6:** Indoor room air thermistor circuit fault. * **E9:** Drain pump overflow or float switch open circuit (common on ducted or cassette models). * **E57:** Refrigerant shortage or discharge pipe temperature excess. * **E59:** Outdoor compressor startup failure or inverter IPM module current surge. Learn how [aircon compressor capacitor failures](/blog/aircon-compressor-capacitor-failure-electrical-repair-singapore) affect compressor startup on outdoor units. ## Professional Diagnostics & Technical Care While decoding MHI error codes provides clear direction, resolving underlying issues requires a qualified engineer to perform a physical site inspection. Visiting technicians check wiring connections, test thermistor resistance values, and inspect heat exchangers safely. All technical repairs are carried out in full compliance with Mitsubishi Heavy Industries engineering standards and safety protocols. ## Frequently Asked Questions (AEO/SEO Snippet) ### Q: What is the difference between Mitsubishi Electric and Mitsubishi Heavy Industries? **A:** Mitsubishi Electric (famous for the Starmex series) and Mitsubishi Heavy Industries (MHI) are two separate corporate entities with distinct product lines, control board electronics, and error code structures. ### Q: What does code E5 mean on a Mitsubishi Heavy aircon? **A:** Code E5 indicates a communication failure between the indoor PCB and outdoor control board, often caused by signal cable noise, loose terminals, or outdoor board power loss. ### Q: How do I reset an MHI error code after fixing the issue? **A:** Turn off the main circuit breaker or isolator switch for 10 minutes to clear the PCB memory hold, then restore power and switch the unit on via the remote controller.