The day has been very cold and damp when a customer calls the dispatcher and says that the coil on her heat pump is frozen solid. The fan is making a noise, which called her attention to the frozen coil. Bob tells the dispatcher, "Call her back and tell her to switch the thermostat setting over to emergency heat." Bob has other calls to make before he will be able to get to the frozen heat pump.
When Bob arrives, the customer meets him at the door and tells him that it is getting cold in the house and asks why the emergency heat did not heat the house up to temperature.