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DIY ‑ Heat Pump Defrost Cycle

When the outside temperature is below 42 degrees, which isn’t the norm in Phoenix, Arizona, but when it does happen, it is common for a heat pump to have some ice buildup and need to be defrosted. Many of our customers are not familiar with this process. The following is what you can expect to experience during a defrost cycle:


  1. You may or may not hear a loud swishing noise as the system goes into and out of the defrost cycle.
  2. Compressor can sound louder than normal.
  3. The outdoor motor will shut off during the defrost cycle.
  4. As the outdoor unit defrosts, you may see steam from the unit.
  5. The machine will shed water onto the roof and or ground by the unit. This water is distilled and will not harm the roof.


  1. It’s normal to feel cold air coming through the supply vents during a defrost cycle (unit in a/c mode)
  2. During the defrost cycle; do not turn off the thermostat. This can delay the defrost cycle, as it can last up to 20 minutes.
  3. Your thermostat may drop a few degrees depending on the length of the defrost cycle (this is normal).
  4. After system has gone thru a defrost cycle, it will return to heating.

Heat pumps are great at maintaining a temperature but will not raise temperature in the house as rapidly as a gas or electric furnace.

During the cold winter nights and mornings it is best to keep your thermostat at a consistent comfortable temperature. We recommend between 69-72 degrees. The key thing to remember about your heat pump is to set it and forget it!

If you have questions about any of this, please call our heating and air conditioning customer service line to discuss further, or schedule an appointment with one of our trained technicians.