Indoor Thermistor Fault (Coil or Room)

What does 2-time blink 2.5-second OFF mean?

This indicates a short or open circuit in either the indoor coil thermistor or the room temperature thermistor. The fault affects the unit's ability to accurately monitor internal temperatures, potentially leading to issues like coil freezing, improper defrost cycles, or inaccurate temperature control. If left unaddressed, this can cause operational inefficiency and damage to the refrigeration system.

• Thermistor RT1 (Room Air) or RT2 (Coil) wiring harness damaged (e.g., pinched, cut) causing an open circuit.
• Contamination or corrosion at thermistor RT1/RT2 connector pins (e.g., J501, J502 on indoor P.C. board) leading to intermittent contact or high resistance.
• Internal failure of thermistor RT1 or RT2 (e.g., cracked epoxy, element degradation) resulting in an out-of-spec resistance value.
• Electrostatic discharge (ESD) or voltage spike damaging the thermistor input circuit on the indoor control P.C. board.

Click steps to track your progress.

1. 1

   Power down the indoor unit by disconnecting the main power supply (L1, L2).

2. 2

   Locate thermistor RT1 (Room Air) and RT2 (Coil) connections on the indoor P.C. board (e.g., J501, J502).

3. 3

   Disconnect thermistor RT1 and RT2. Measure the resistance of each thermistor using a multimeter. Compare readings to the manufacturer's specified temperature-resistance curve (e.g., 10kΩ at 25°C).

4. 4

   Inspect the wiring harnesses for RT1 and RT2 for physical damage, shorts, or opens. Check continuity from the thermistor to the P.C. board connector pins.

5. 5

   Clean thermistor connectors and P.C. board receptacles using electrical contact cleaner. Reconnect and secure all connections.

6. 6

   If thermistor resistance is out of spec or wiring is damaged, replace the faulty thermistor (RT1 or RT2) or repair the wiring harness. Restore power and monitor unit operation.