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.

When this check determines that the DFT is closed and not the problem, you use a jumper at the “Speed Up” pins to manually initiate a defrost mode, and note that the reversing valve functions properly, but the OFM (Outdoor Fan Motor) continues to operate.

This leads you to check at the OF1 and OF2 terminals of the DR (Defrost Relay), which indicates that the contacts are closed.         

You troubleshooting question: What is the next step you need to take to get this unit operating properly?      

Submit your answer here.

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