Troubleshooting a Trane Heat Pump Defrost

The Trane heat pump defrost protects your heat pump in cold weather.

The Trane heat pump defrost is controlled by a defrost control board. Its purpose is to detect when the outside air is likely to cause the heat pump's outside coil to frost over. When the sensors on the control board detect frosting temperatures, the heat pump defrost kicks on, protecting the coil. The defrost will not initiate unless the outside air is below 52 degrees and the coil is 35 degrees or below. If the defrost does not kick on, you can test the board to see if it is faulty.

Instructions

1. Unscrew and remove the back panel of the heat pump's outside unit.

2. Locate the defrost control board. The defrost board has four metal test pins sticking out at the bottom of a green circuit board.

3. Lay a screwdriver sideways across the "Test Common" pin and the "TST" pin at the same time. This will jump the defrost and speed up the timing.

4. Remove the screwdriver.

5. Make sure the heat pump is running in heat mode.

6. Lay a screwdriver sideways across the "Test Common" pin and the "FRC-DFT" pin at the same time. This will force a defrost cycle to begin.

7. Remove the screwdriver after the defrost cycle starts. If the defrost cycle does not start, it's time to replace the board.

References

• Alan Boleware; Service Technician, Complete Air and Heat, Inc.; Indian Harbour Beach, Fla.
• Trane Service Guide; Trane Inc; 2010