New Goodman heat pump. The Goodman installer suited me better than the installers of some other brands. The difference was more than price. The installation is first class. The outdoor unit fan does not run while defrosting, which I think is a good feature. But recently the unit had not been running for several minutes and when it started, it was in defrost mode for the first moments and then switched to heat mode. Does this seem normal? How does this unit sense or "decide" when to defrost?