Mitsubishi Electric Mini-Split Code U2
Soft lockout
Abnormal high discharge temperature or high compressor surface temperature, which usually means the system is short of refrigerant. The discharge thermistor TH4 exceeded 230F for 5 minutes, or the compressor surface thermistor TH33 exceeded 257F.
Manual wording: “Abnormal high discharge temperature, shortage of refrigerant ... Abnormal if TH4 exceeds 230F [110C] or more continuously for 30 seconds”
Documented for: A-Control outdoor units (PUZ, MUZ, MXZ)
Likely causes, most common first
- Shortage of refrigerant
- Defective operation of the stop valve (not fully open)
- Defective action of the linear expansion valve
- Clogging with foreign objects in the refrigerant circuit
- Defective discharge or compressor-surface thermistor
- Defective outdoor controller board
What you can safely check yourself
- Check the outdoor unit is clear of snow, ice and debris
- Turn the system off at the breaker, wait one minute, and turn it back on once
When to call a technician
This code points at a refrigerant charge or expansion valve problem. Refrigerant work requires EPA certification and gauges. Call a technician.
A Mitsubishi Electric mini-split throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Source
- Service Manual No. OCH750 Revised Edition-E - PUZ-HA Outdoor Units (May 2024) (Mitsubishi Electric, PUZ-HA24NHA1, PUZ-HA30NKA, PUZ-HA36NKA, PUZ-HA42NKA1 heat-pump outdoor units) · checked 2026-08-25