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Mitsubishi · Heat pump

P9 Coil sensor TH5 open or shorted

Medium severity Mr. Slim PEAD-RP JA(L) ducted indoor unit

What the control is telling you

The condenser/evaporator thermistor TH5 reads 90°C or more, or -40°C or less, and does not recover after 3 minutes. Checked in cool, dry and heat (not during defrost).

Applies to: PEAD-RP35/50/60/71/100/125/140JA and JA(L) ducted indoor units (220-240 V models)

Likely causes

  • TH5 thermistor out of range
  • Loose connector CN44 on the indoor control board
  • Broken wire in the thermistor lead
  • Refrigerant circuit problem driving the coil temperature to an extreme
  • Faulty indoor control board

Test and repair steps

  1. Turn the unit off at the remote first, then switch off the breaker before opening the unit or unplugging connectors.
  2. Unplug TH5 at CN44 and measure it. Thermistor values (approx.): 0°C 15 kΩ, 10°C 9.6 kΩ, 20°C 6.3 kΩ, 25°C 5.2 kΩ, 30°C 4.3 kΩ, 40°C 3.0 kΩ. Open or short = bad sensor.
  3. Reseat CN44 and retry.
  4. In test mode, read the coil temperature on the remote. Extreme readings with a good sensor point to a refrigerant problem.
  5. If nothing above is wrong, replace the indoor board.
  6. After the repair, cycle the power and run the unit to confirm the code does not come back.

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Source: Mitsubishi Electric PEAD-RP35-140JA(L) Service Manual, 10-3 Self-diagnosis action table, p.33. Summarized in our own words; check the original manual for your model.

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For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.