P1 Room (intake) air sensor TH1 open or shorted

What the control is telling you

The board reads the return-air thermistor as shorted (90°C or more) or open (-40°C or less). The unit first pauses for 3 minutes and only shows P1 if the reading is still bad. Checked in cool, dry and heat.

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

Likely causes

• TH1 thermistor out of range
• Loose or badly seated connector CN20 on the indoor control board
• Broken wire or poor crimp in the thermistor lead
• 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 TH1 at CN20 and measure its resistance. 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. Flex the lead while measuring - a reading that jumps points to a broken wire.
4. Reseat CN20 firmly and power up again to see if the code clears.
5. If the sensor checks good, compare the room temperature shown on the remote (service mode) with a real thermometer; a big difference means the indoor board is faulty.
6. After the repair, cycle the power and run the unit to confirm the code does not come back.