Icing is a condition where the evaporator coil for the air conditioner ices over and your unit no longer can cool the home properly. The evaporator coil is located in the ductwork, usually just above your furnace. Your furnace fan moves air over the coil and distributes the cool air throughout your home.
Often if an air conditioner is icing, it can be traced to improper use. This is a common problem for new home owners and it is easy to fix.
If you set the thermostat too low, it can cause the unit to ice. Many people think that by setting a lower temperature it will help to cool down the home faster. That is not how your air conditioner works. If you set the temperature too low, your air conditioner will run continuously trying to get your house to the temperature you set.
The volume and temperature of the air flowing through the coil affects the surface temperature of the coil. As the temperature in the home drops the lower temperature of the air flowing over the coil is not sufficient to keep the surface temperature of the coil, which is being cooled by the refrigerant, above freezing. As a result, the water on the coil (condensate) freezes and air can no longer flow through the coil. Evaporator coil freezing can also occur if the outside temperature drops quickly and the air conditioner is left running to cool down the home. We often see this if the thermostat is set too low or the AC was left off all day and turned on in the evening to cool the house down. If there is a change in the weather and the outside temperature drops quickly the refrigerant temperature at the evaporator coil is so low, it can cause the moisture on the coil to freeze.
Your air conditioner coil will ice if there is not proper air flow over the coil. Some people close too many vents in an effort to drive cool air to the second floor of their home. Closing vents restricts air flow, which can cause your unit to ice.
A dirty furnace filter can also cause your unit to ice. Dirty filters are another cause of restricted air flow.
What To Do When Your AC Ices:
- Turn off the air conditioner. It has to thaw out and cannot do this while it is running.
- Make sure all your vents are open.
- Make sure you have a clean furnace filter installed.
- Change your furnace fan setting from ‘auto’ to ‘on’. This will thaw the coil faster.
- Wait a few hours for the ice to thaw from the coil. Set the temperature at a reasonable level (72-75° F) (22-24°C) and start up your air conditioner again.
If these steps don't solve the problem, it's time for a service call.
A low refrigerant charge can also cause icing or frosting but it will require a mechanic to check the system pressures to confirm this.