Room temperature sensor error: the room-temperature thermistor is open or shorted. The operation lamp blinks 4 times and the timer lamp blinks once.
Fujitsu 41 is the room temperature thermistor open or short. The lamps blink 4 and then 1. Code 42 blinks 4 and then 2 and is the indoor heat exchanger sensor. Do not use the 41 page for a 4-and-2 blink.
Likely causes
- Connector loose, removed, or miswired
- Thermistor failed open or short
- Indoor unit main PCB failure
Safe checks for 41
- Switch the breaker off and leave the indoor unit closed. The sensor is inside the unit
- Technicianthe manual checks the thermistor connector and its resistance, then the board
Capacitors can hold a charge after the power is off. Safety terms.
When to call a pro
Code 41 is the room sensor, not the heat-exchanger sensor (code 42, which blinks 4 and then 2). Call a licensed HVAC technician.
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