As we head towards the cooler weather, we’re here to help explain what the defrost cycle is, and why it occurs as part of the normal heating operation of air conditioning

During the colder winter months, reverse cycle air conditioners will, at some point during heating operation, perform a defrost cycle, but what is it, and why does it occur?

When using heating mode, a reverse cycle air conditioner extracts heat from the air outside and transfers it inside your premises to warm it.  Defrosting can start when the temperature of your outdoor heat exchanger becomes too low (around 0` or below and the moisture in the air starts to freeze on its surface.  The sensors in the outdoor unit detect ice has started forming on the heat exchanger and the system starts to try to remove this ice before it builds up, causing the indoor and outdoor fans to stop but leaving the compressor to keep running and melt the frost away.  This mode will continue until the temperature of your outdoor heat exchanger rises and the ice melts

Some owners can feel that this is a fault because it isn’t heating as well as it should, but it is important to remember that defrosting is a normal part of the heating operation and is not a fault with the product.

Below are some of the frequently asked questions about the defrost cycle.


Why does my unit have to do a defrost cycle?

Any ice build up on the outside heat exchanger will reduce airflow across the heat exchanger, this reduces the efficiency, the more ice build-up the more it is reduced.  In extreme cases, this can also cause damage to the outdoor unit.

How do I tell if my unit is in a defrost cycle?

Inside you will notice the unit will stop heating, the indoor fan will stop and depending in the model, there will be some form of visual indication such as a message on your wall control indicating heat standby or defrost.  Outside, the outdoor fan will also have stopped but the compressor will be running.

How often will my unit go into defrost mode?

There are several factors that influence how often a unit will go into defrost mode.  Some of these include, but aren’t limited to:

  • The outdoor temperature and humidity
  • The amount of heating required
  • The condition and cleanliness of the system

Is there any way I can help to reduce defrosting?

Yes there is.

  • Keep your unit well maintained and ensure you are operating it correctly
  • Don’t have the thermostat set too high.  The less load you place on the unit the less frequently it will need to defrost in cold conditions
  • Ultimately, permanent fixes such as installing insulation in ceilings, wall s and under floors will help reduce your heating requirements (and save you money).  More immediately, keeping doors closed and curtains drawn will also help to reduce your heating requirements
  • Make sure there are no barriers erected out the outdoor unit
  • Raise the outdoor unit off the ground by at least 100mm, by doing this the outdoor unit isn’t sitting in a pool of cold, moist air