Where is the defrost sensor located?

The defrost sensor—often referred to as the defrost thermostat or outdoor coil temperature sensor—is typically located directly on the outdoor condensing unit, clipped onto or inserted into the copper tubing of the outdoor coil fins. Its precise position allows it to monitor the exact temperature of the coil during cold weather heating operations so the defrost control board knows when to initiate a defrost cycle. If the sensor becomes dislodged, damaged, or coated in dirt, it may fail to communicate correct temperature data, causing the heat pump to either ice up completely or enter endless, unnecessary defrost cycles. Locating the sensor requires removing the exterior service access panel of the outdoor unit while electrical power is turned off at the breaker. You can verify the sensor's integrity and wiring continuity using a digital multimeter.