Error F1, F2, or F3 on Air Conditioners: Temperature Sensor Faults and Fixes
When an air conditioner displays error codes F1, F2, or F3, it is signaling a fault with its internal NTC temperature thermistor sensors. These sensitive electronic probes monitor room ambient air temperature, indoor evaporator coil temperature, and outdoor condenser discharge temperatures to regulate cooling cycles.
What Each Fault Code Means
Error F1: Indoor Room Ambient Temperature Sensor Open or Short-Circuited.
Error F2: Indoor Evaporator Coil Pipe Temperature Sensor (Copper Tube Thermistor) Fault.
Error F3: Outdoor Condenser Temperature Sensor or Compressor Discharge Probe Fault.
How to Test an NTC Thermistor Sensor with a Multimeter
1. Switch off power to the AC unit.
2. Open the indoor split casing to locate the sensor wiring connected to the main control board.
3. Unplug the 2-pin sensor terminal.
4. Set a digital multimeter to resistance mode (20k Ohms) and probe the two terminals. At 25°C (77°F), standard HVAC thermistors should read 5kΩ, 10kΩ, or 15kΩ (depending on manufacturer specification).
5. If the multimeter reads 0Ω (short circuit) or infinite (open circuit), the probe is dead and must be replaced.
Replacing an NTC Sensor
Replacing an NTC sensor is an inexpensive €40-€80 repair. The old probe is unclipped from the copper pipe socket, thermal paste is applied, and the new sensor is plugged into the PCB header.
FAQ
Can dirty filters trigger error F2?
Yes. If severe filter blockages cause the indoor coil to freeze into a block of ice, the copper pipe sensor records sub-zero temperatures, triggering abnormal temperature alerts.
Are HVAC temperature sensors universal?
No. You must install a thermistor with the exact nominal resistance curve (5k, 10k, 15k, or 20k) specified by the equipment manufacturer.