Mitsubishi Electric Mini-Split Code P9
Soft lockout
Pipe temperature thermistor / condenser-evaporator (TH5) error. The indoor gas-line sensor reads short circuit (194F or more) or open circuit (-40F or less).
Manual wording: “Pipe temperature thermistor/Condenser-Evaporator (TH5) ... Short: 90C [194F] or more, Open: -40C [-40F] or less”
Documented for: A-Control indoor units (PKA-A, PLA-A, PEAD-A and M-Series with a wired controller)
Likely causes, most common first
- Defective thermistor characteristics
- Contact failure of connector CN44 on the indoor controller board (insert failure)
- Breaking of wire or contact failure of thermistor wiring
- Thermistor driven past 194F or below -40F by a defective refrigerant circuit
- Defective indoor controller board
What you can safely check yourself
- Turn the system off at the breaker, wait one minute, and turn it back on once to see if it resets
When to call a technician
Thermistor testing happens at the indoor control board. 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.
Sources
- Indoor Unit Service Manual No. OCH761 Revised Edition-A - PKA-A LA Series (May 2021) (Mitsubishi Electric, PKA-A12LA, PKA-A18LA, PKA-A12LA.TH, PKA-A18LA.TH wall-mounted indoor units) · checked 2026-08-25
- 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