What It Means
Open or short circuit fault detected on outdoor unit thermistors.
Mitsubishi Electric All Systems
Mitsubishi Electric Error Code U3 – U4
Troubleshooting guide for the Mitsubishi Electric system fault U3 – U4.
ACLogics Fix Mitsubishi Electric code U3 – U4 See how ACLogics handles it → Fix U3 – U4 step-by-step
Possible Causes
- Outdoor unit thermistor open or short circuit.
- Outdoor thermistor harness or connector fault.
Not sure which one it is — or if it's none of these? Try ACLogics today.
Disclaimer: This information is for general reference. Error codes can vary by model and production year. Always refer to your machine's specific manual and the information printed on the unit itself.
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Full Diagnosis
Open/short of outdoor unit thermistors.
All Recorded Causes
Verify Before Replacing Parts
- Confirm the exact Mitsubishi Electric model family and default context before acting on a generic code description.
- Verify the sensor or thermistor reading against the expected range for the current operating condition, keeping in mind that the most likely cause listed above.
- Check the sensor harness and board connection before condemning the sensor itself; on Mitsubishi Electric units this is also where you'd confirm the next candidate on the list.
- After the correction, run the system long enough to confirm the default fault does not return under normal load.
Not sure which system this Mitsubishi Electric code is on?
ACLogics has guided diagnostics for 73 Mitsubishi Electric fault codes and asks the right questions to narrow it down.
