Troubleshooting Puzzle: A Heat Pump with a Frosted Outdoor Coil
Your troubleshooting situation this month involves a complaint from a customer about their heat pump that’s not working. When you arrive, you find the thermostat set at 70°F, while the indoor temperature is only at 64°. The customer says that the unit has been running constantly for several hours without shutting off.
When you check the outdoor unit, you find the coil completely frosted, and the compressor and outdoor fan motor running. These observations lead you to perform a voltage check across the terminals of the DFT (Defrost Termination Thermostat) shown in the bottom right-hand corner of the pictorial diagram in Figure One.