Your Heat Pump: Its Cooling, Heating and Defrost Cycles

Your heat pump uses a straightforward process to heat your home on chilly nights and keep you comfortable during the scorching summer. Your heat pump has three cycles: cooling, heating and defrost. This is what happens during those three cycles.

The cooling cycle:

  • Liquid refrigerant goes through an expansion device and becomes a low-pressure mixture of liquid and vapor. The refrigerant then moves to the evaporator coil, where it absorbs heat form the indoor air and comes to a boil. At this point, the refrigerant becomes a low-temperature vapor.
  • The vapor goes through the reversing valve–the device that allows your heat pump to both heat and cool–and continues on to the compressor. There, it heats up as it is compressed.
  • The hot gas goes through the reversing valve and continues along to the condenser coil. It is then released outside. The refrigerant once again becomes a liquid. It returns to the expansion device, and the cycle continues.

The heating cycle:

  • The liquid refrigerant goes through the expansion device before moving along to the evaporator coil. The refrigerant then absorbs heat from the outdoor air and comes to a boil. At that point, it vaporizes.
  • The refrigerant vapor goes through the reversing valve and enters the compressor. It heats up as it is compressed.
  • After leaving the reversing valve, the hot gas goes to the indoor condenser coil. The heat from the hot gas is released inside your home. This causes the refrigerant to become a liquid. The liquid returns to the expansion device, and the cycle continues.

The defrost cycle:

  • This cycle happens when the outside temperature is at or near freezing—a rarity in San Antonio. At this temperature, frost can form on the outside coil during the heating cycle, reducing efficiency.
  • The reversing valve switches to cooling mode. This sends hot gas to the outdoor coil to melt any the frost. At the same time, the outdoor fan goes off to reduce the heat needed to melt the frost, and the heat pump cools the air in the ductwork.

Think you’ll soon need to replace your heat pump? Contact Beyer Boys. We can help you find the system that’s ideally suited to your San Antonio-area home, and we can ensure that it’s properly installed and maintained.

Our goal is to help educate our customers in the greater San Antonio, Texas area about energy and home comfort issues (specific to HVAC systems).