What happens when a Heat Pump goes into defrost and why!

A Heat Pump may go into defrost when you turn on your heat. Instead of the refrigerant cooling your house down the refrigerant heats up your house. In the cooling cycle heat is absorbed from your house by the refrigerant and discharged to the outside by your outside unit. In the heating cycle heat is absorbed from the outside air and discharged into your house by the inside unit. In the heating cycle as the temperature decreases outside your unit works harder and harder to absorb heat from the outside air and at around 40 degrees your outside unit starts to form ice on the outside coil. At a predetermined time your outside unit senses that there is too much ice on the outside coil and the unit goes into defrost cycle. At this time this is what happens. The refrigerant cycle reverses and goes into the cooling mode. The outside unit shuts the outside fan motor off and the outside coil starts to defrost at the same time the auxiliary heat strip comes on to temper the cool air coming out of the grills. As the outside coil is defrosting you may see steam coming off the outside unit. Some people think this is smoke and their unit is on fire, not so! The defrost cycle lasts 30 to 45 minutes and when the unit sensors sense the ice has melted the unit then reverses into the heat mode, the condenser fan motor starts and the auxiliary heat goes off. Now if the unit in the heat mode can not keep the house warm as the temperature drops outside the auxiliary heat comes on to help the heat pump maintain inside house temperature. If after a period of time the unit does not hold temperature in the house you may need to get more heat capacity for your house. This is the time you call for a heat load specialist to come to your house and do a heat load calculation to determine how much more heat is needed to make your house comfortable.