Indoor air conditioner units are often part of a switch-unit with a built-in furnace. In ideal operation conditions, an air conditioner unit produces a constant flow of cool air to the home. The air is cooled via a refrigerant agent known as coolant, which is pumped through the unit through a system of tubes and pipes. When the unit is functioning properly, there is no build up or accumulation, but there are issues which can crop up that lead to the unit building up ice and freezing as opposed to cooling the home. Filters Air conditioners and furnaces rely on airflow to push the air through the vents that cool and heat a home. In both cases, the filters on the outside of the unit are there to ensure proper airflow and restrict debris from entering the unit. If these filters ever become blocked, the restricted airflow leads to ice building up inside of the air conditioner because it isn’t being cycled out into the vents fast enough. The longer this goes on, the more ice that builds up, until the point the unit completely freezes.

For best results, always clean the air filters every few months. Evaporator Coils Evaporator coils in an air conditioner are there to help with heat exchange, absorbing heat that needs to be cooled down. The evaporator coils are filled with the coolant from the air conditioner, and cool the air that passes through. Over time, these coils collect dust and debris just like the air filters. As this debris builds up, the effectiveness of the unit is compromised. Over time as more dirt accumulates, the coils no longer function properly, and rather than cooling off the air, they begin to build up frost and freeze. carrier central air conditioning dealersClean the coils every few months for best results. water leak from ac unitRefrigerant Issues When everything within an air conditioner is working perfectly, the coolant in the reservoir lasts a lifetime and beyond, as they are built to last, not to leak, and the coolant is continually recycled without ever being used up. hvac unit 17 review questions

However, leaks can occur, either through faulty installation or through breakdown of other components within the interior over time. When low levels of coolant occur, ice buildup and freezing can occur as the unit tries to work overtime to produce cooler air. Leaking coolant is also another cause of ice buildup and eventual freezing of the unit. Having a licensed technician inspect the unit and repair the leak/refill the coolant reservoir is the only option. Outside Temperature Air conditioners work best in temperatures above 60 degrees. If the exterior temperatures are too low, the coils within the unit are colder than they would be in summer/hot weather, which leads to the air conditioner coils refrigerating the room air, rather than just the air within the unit itself. This leads to ice buildup and freezing. The problem tends to be more prevalent at night than during the daytime hours and is easily solved by simply switching the unit to “Fan” mode to let it circulate the cold air until the ice melts away.

Photo Credits Jupiterimages/Comstock/Getty Images Suggest a Correction The outdoor unit of a heat pump (that metal noisemaker that disturbs the peace on so many otherwise nice summer afternoons) will occasionally grow frost around the outside of the unit when it's in heating mode. If so, how much is OK? What about the amount of frost on the unit in this photo? Yes, a little bit of frost on the heat pump's outdoor unit is normal. No, the amount of frost you see above is not OK. Why does it happen? It's just the science of phase changes. Outdoor air—yes, even cold, dry outdoor air—has some water vapor in it. Air with water vapor in it has a dew point, the temperature at which the water vapor changes phase and becomes a liquid. When that outdoor air finds a surface that's at a temperature below its dew point, the water vapor condense out of it. If that surface and the surrounding air are below the freezing point as well, the condensed water freezes. All that depends on the outdoor air and the temperature of the heat pump condenser.

The refrigerant in a heat pump typically runs 10 to 20 degrees Fahrenheit colder than the outdoor air. If that temperatures happens to be below the dew point of the air and below the freezing point, you get frost. The typical conditions for this to occur are when the outdoor air temperature is below 40° F and the relative humidity is about 70% or higher. As the temperature drops below 20° F, the formation of frost diminishes. As I write this, heat pumps in Atlanta may well be frosting up a bit. The temperature is 39° F and the RH is 65%. How much frost is too much? If you see a little bit of frost forming, check back in a while and see if it's still there. Heat pumps have a defrost cycle that melts frost that builds up. The defrost cycle simply changes the direction of flow so that the hot refrigerant doesn't take its heat indoors but instead goes back through the outdoor coil. The fan in the outdoor unit stops to keep cold air from hindering the defrosting process. A little bit of frost is OK as long as it disappears after a while.

If you see so much frost on the unit that air cannot pass through the fins on the outdoor unit, as in the photo above, or if frost stays on the coil for a two hours or more, then something is wrong. It could be the defrost controls, the reversing valve (shown in photo at right), or improper refrigerant level. If frost forms on the outdoor unit and stays there, it's time to call your HVAC company and have them repair the system. The defrost cycle on a heat pump can use a lot of energy. When the refrigerant flows backwards to defrost the outdoor coil, it's not heating the house. In fact, without supplemental heat, your system will blow cold air into your home. Most heat pumps have supplemental heat, though, and most of the time it's electric resistance heat. In the defrost cycle, your supplemental heat kicks in and you pay more. But how smart is the defrost system on your heat pump? Does it go into defrost mode only when necessary? Or does it cycle on and off even when it doesn't need to?