I can understand why the outside unit coil fan on my heat pump runs in the summer to disperse the heat that is being pulled from indoors. Can someone explain why the outside unit coil fan needs to run in the winter when the heat pump is in heat mode? Thanks

 

In the summer..... the evaporator coil extracts the heat from inside your home and discharges it outside via the condenser. In the winter..... the refrigerant flow is reversed and your condenser outside extracts heat from the cold air and discharges it inside via the evaporator.

When in heating mode..... every so often based on condenser coil temperatures or a timed run period ...... the unit will go into defrost. Basically that's the system running in A/C mode. It takes heat from inside the house to defrost the outside coil. During the defrost period.... the outside fan doesn't always run.