Mitsubishi Error Code U3: Discharge Thermistor Short/Open
Warning: Your Mitsubishi HVAC system has detected a potential issue with the discharge thermistor, which could lead to system damage if not addressed.
How to Fix Mitsubishi Code U3
- Turn off your HVAC system at the thermostat and the circuit breaker to prevent further system operation.
- Contact a professional HVAC technician to diagnose and repair the issue.
How to Reset Mitsubishi Code U3
- Turn off the unit using the remote control or wall controller.
- Turn off the circuit breaker for the outdoor and indoor units. Wait 60 seconds.
- Restore power at the breaker.
- Turn the unit on with the remote control. If the error returns, the fault needs professional diagnosis.
What does U3 mean?
The U3 error code on your Mitsubishi HVAC system indicates a problem with the discharge thermistor. This component measures the temperature of the air leaving your system, helping to maintain optimal cooling and heating. If the thermistor is shorted or open (not functioning), your system can't accurately monitor this temperature, leading to inefficient operation and potential system damage. Your system has entered a lockout mode to prevent further issues.
Affected Models
Replacement Parts
| Part | OEM Number | Est. Cost |
|---|---|---|
| Discharge Thermistor | — | — |
Related Codes on Same Models
| Code | Description | Severity |
|---|---|---|
| 1 | Indoor/Outdoor Mismatch | Warning |
| 2 | Power Supply Phase Error | Warning |
| 3 | Communication Error | Warning |
| 4 | Inverter Error | Warning |
| 5 | Outdoor Thermistor Open/Short | Warning |
| 6 | Indoor Freeze/Overheat | Warning |
| 7 | Outdoor Freeze/Overheat | Warning |
| E6 | Indoor/Outdoor Communication Error | Warning |
| E9 | Indoor/Outdoor Communication Fault | Warning |
| P1 | Intake Sensor Error | Warning |