ENERGY BOOMER: WHY DOES MY AIR CONDITIONER EVAPORATOR COIL FREEZE?

If the evaporator coil, on your air conditioner, starts making ice, it will still run. When it ices up it runs but does not cool the house. The evaporator coil is the cold part of the air conditioner.

The evaporator coil is hidden inside the ductwork above your furnace in a central air conditioning system. On a window or split unit, the evaporator coil is the part inside the house.

A frozen evaporator costs money on your electric bill.

When the evaporator coil freezes, the air conditioner continues to run wasting energy. It does not cool the house it just makes more ice.

If evaporator coil did not freeze until after your unit was serviced, it is likely that the service technician put in too much refrigerant.

Too much or too little refrigerant makes air conditioners work inefficiently, wasting your money. Too much refrigerant can cause icing of the evaporator coil.

If your air conditioner has always made ice or only makes ice some of the time, the problem is likely to be airflow.

The evaporator coil needs to have enough warm air passing through it to keep it from freezing. If the air is not warm enough or there is not enough airflow, the evaporator temperature will drop below freezing.

An air conditioner is not a refrigeration unit.

If you try to make the air in your house too cool, it will not be able to keep the evaporator coil above freezing. Air conditioners are designed to make a house no colder than 72 degrees. Set your thermostat at 74 degrees or higher and the evaporator should not freeze.

If your evaporator coil still freezes when the thermostat is set at 74 or higher, then you may have an airflow problem. The evaporator needs to have enough warm air passing through it to keep it above freezing.

Replace dirty air filters to help the airflow.
Make sure all outlets are open and that the registers are not blocked. You must keep newspapers, magazines and furniture off the air outlets to allow full airflow.
Make sure all return air grills are open and clean.
Clean the coil of the evaporator to help the air flow through.
Make sure that dampers inside of the ductwork do not choke the airflow.

An oversize air conditioner may be the cause of freezing.

The problem may be the air conditioner is so over size that the rest of the system cannot provide enough airflow. The bigger the air conditioner the more airflow it needs to keep from freezing up.

To keep the evaporator above freezing, you may need to change some equipment. Possibilities include speeding up the air mover blower (furnace fan), installing a register booster fan or up sizing the ductwork.

Another possibility is to have an electrician add a clip on thermostat to the evaporator coil. It will shut the air conditioner off when the temperature nears freezing. The air conditioner will cycle on and off more often but it will not freeze.

Good Luck.