Deice Mode on your Air Conditioning System What is a “defrost cycle” or “deice mode”? In heating mode a heat pump extracts heat from the outside air and transfers it inside your premises to warm it. When the ambient temperature outside gets very cold (close to 0 degrees or below) the moisture in the air freezes on the outdoor unit’s heat exchanger as the fan blows the air across it. A defrost cycle is simply the system recognising that ice has formed or begun to form and automatically fixing this. It is important not to stop the unit before the defrost cycle has ended, because if the unit is restarted shortly afterwards it will run very inefficiently and may cause damage to itself. Why does my unit have to do a defrost cycle? Any ice building up on the outside heat exchanger reduces the airflow across it, which will effect the efficiency, sometimes reducing it dramatically. 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. Outside, the outdoor fan will also have stopped and the compressor will be running. There will be a puddle of water under and around the outdoor unit. A couple of things you may notice your air conditioning doing now you have switched it to heating A loud whooshing sound just before the indoor fan stops. This is the system cycling off on thermostat or going into de-ice mode Seeing what appears to be smoke coming from the outdoor unit. This is actually steam coming off in de-ice mode. It is quite a common occurrence during the colder weather The outdoor unit (condensing unit) will create a lot of water. The outdoor unit can get quite icy as well, even to the point that it is totally white with frost.Now, I have to ask...ice or frost? A layer of frost is not a problem, most units are factory programmed to 'de-frost' about every 90 minutes. A layer of ice is a problem.  This invariably is a dilemma with heat pumps. 

It's probably a malfunctioning defrost control which could cost between $350 and $1,000 to replace. The temporary fixes you can try prior to your service technician arriving are: Go to your thermostat and switch it to 'cooling'.  This puts the unit effectively into defrost mode.  Once the ice has melted, return it to the heat position. String some Christmas lights on the unit, the warmth from the bulbs will keep the ice from forming.  Do not use the new LED Lights for this, they don't generate enough heat to work.  Make sure this string of lights is plugged into a GFCI protected circuit. Shine large workshop type spotlights onto the unit. Know this about your heat pump: On a cold, wet morning it is only going to warm your inside air about 20 degrees when measured at the supply register.  That means if your thermostat is set at 70 degrees and your unit is maintaining that temperature, the air temp at the supply register won't be over 90 degrees. That's cooler than your body temperature, it will not feel like the heat is on.

For that reason, we tell people never adjust the heat pump thermostat throughout the day.  You cannot wake up in the morning and ask your unit to raise the temperature while you get ready for work and then drop the setting to let it rest while you are gone.central air conditioning unit not cooling problem For heat pumps in winter, pick a livable temperature and leave it there until the spring, it is how the unit was designed to work.window ac unit falling out Our thanks to Green Valley Heating and Cooling and Yavapai Heating and Cooling for their photos.ac units split unitsIce storage is a clean, reliable and least-cost distributed energy storage solution for the grid. Since 2005, Ice Bears have been installed in more than 40 utility services, transforming inefficient and polluting air conditioners into efficient and clean cooling systems.

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