Mitsubishi air conditioning systems—particularly the highly popular Starmex series—are renowned for their reliability, quiet operation, and energy efficiency in Singapore homes. However, when a system encounters an anomaly, it communicates the issue via error codes displayed on the indoor unit’s LED indicator flashes or the wired controller. Understanding these codes helps you identify whether a simple reset or immediate professional repair is needed.
1. Overview & Error Categories
Mitsubishi aircon codes are categorized based on where the fault originates:
- P Series (Indoor Unit & Protection Codes): Relates to indoor sensors, drainage systems, fan motors, and freeze/overheat safeguards.
- E Series (Communication & Transmission Codes): Indicates signal transmission breakdowns between the indoor unit, outdoor unit, or remote controller.
- U Series (Outdoor & Compressor Protection Codes): Pertains to outdoor thermistors, high/low pressure triggers, compressor overcurrent, and discharge temperatures.
- F Series (Control & Phase Faults): Covers power supply phase anomalies, input circuits, and indoor memory (EEPROM) errors.
2. Reading & Resetting Your Mitsubishi Display
1.Count the LED Blinks or Check Display:
Count the number of times the operation indicator lamp flashes in a cycle, or read the alphanumeric code directly off your wired controller.
2.Perform a Hard Power Reset:
Shut off the air conditioner at the main wall isolator or circuit breaker box.
3.Wait for System Discharge:
Keep the power off for 5 to 10 minutes to allow internal circuit capacitors to fully discharge and clear temporary glitches.
4.Power Back On:
Turn the isolator back on. If the error code reapperns instantly, a physical or electrical fault is active.
3. Reference Table: Common Mitsubishi Error Codes
| Code / Flash Count | Meaning / Cause | Severity | Recommended Action | Typical SG Cost |
| P1 (1 flash) | Intake room temperature sensor error | Medium | Inspect thermistor connection; replace indoor room sensor. | From $130 |
| P2 / P9 (2 flashes) | Pipe / liquid heat exchanger thermistor error | Medium | Test and replace indoor coil or liquid pipe sensor. | From $130 |
| P4 (4 flashes) | Drain sensor error / Float switch open | Medium | Clean condensate drain pan and clear pipe blockages. | From $90 |
| P5 | Drain pump malfunction | Medium | Clean or replace faulty condensate drain pump. | $150 – $300 |
| P6 (5 flashes) | Freezing (cooling) or overheating (heating) protection | Medium | Clean dirty air filters immediately to restore airflow. | $90 (Standard Clean) |
| E6, E7 (3 flashes) | Indoor/outdoor unit communication error | High | Check outdoor isolator status, terminal wiring, and signal cable integrity. | Diagnostic / $150–$350 |
| U1 / Ud | Abnormal high pressure / overheating safeguard | High | Clear debris around outdoor unit coils; check system pressure. | $90 – $180 |
| U2 | High discharge temp / insufficient refrigerant | High | Conduct pressure test to locate gas leaks and recharge refrigerant. | From $180 |
| U3 / U4 | Outdoor unit thermistor open or short circuit | Medium | Inspect and replace outdoor ambient or coil thermistors. | From $130 |
| U6 / UF | Compressor overcurrent / locked rotor | High | Inspect inverter power module, compressor windings, and power supply. | $300 – $750+ |
4. DIY vs. Professional Repair Matrix
⚠️ Warning: Running your Mitsubishi aircon continuously with active high-severity codes (such as U2, U6, UF, or E6) can lead to severe compressor seizure, burnt inverter boards, or permanent system failure.
🟢 Safe to DIY / Self-Check
- System Power Reset: Executing a 5-minute breaker power cycle to clear minor transient digital faults.
- Filter Maintenance: Washing mesh air filters regularly to prevent ice formation and trigger alerts like P6.
- Isolator Check: Ensuring the outdoor unit power isolator switch is securely turned on to resolve communication drops.
🔴 Requires Professional Repair & Servicing
- Refrigerant & Pressure Work (U1, U2): Nitrogen pressure testing, leak patching, and precise weight-based gas top-ups.
- Sensor & Thermistor Replacements (P1, P2, U3, U4): Resistance testing and swapping damaged internal temperature sensors.
- Electrical & Inverter Diagnostics (U6, E6, UF): High-voltage board analysis, terminal rewiring, and compressor circuit testing.
