BB, were you just looking out the window and noticed the condenser fan not running, or were you outside? Reason I ask is, during defrost, the condenser fan motor doesn't run, only the compressor in A/C cycle (not heat) to defrost the condenser coil, and back-up heat is brought on to compensate inside while defrost is occurring.
Also, not sure of your ambient temps, but sometimes they (installer) have added a thermistor added to prevent operation in extreme cold, since once they (Heat Pump) reach a balance point, they generate little heat while operating, so they're just prevented from operation, and heat is provided 100% from whatever back-up heat source you have. Once ambient temps rise, it allows it to operate again.