AC Temperature Sensor (Thermistor) Failure

Identify fault by sensor location (indoor, evap, outdoor, condenser, discharge)

Check: Thermistor = NTC type, typically 5 kΩ or 10 kΩ at 25°C. Measure resistance → compare with B-constant table (B25/85, typically 3950 or 3435). Open = ∞, short = 0 Ω, drift = ±20% off table. Cable = check open/contact.

What to do: Replace with same spec (resistance + B-constant must match). Mount per location (heat exchanger coil clip or discharge pipe contact). Apply thermal grease for pipe contact. Cable open = new cable or extension. Activate learning mode after replacement (inverter type).