During the heat of summer, central air conditioners sometimes freeze up. When the evaporator coil freezes, it won’t be able to adequately cool your home. If this occurs repeatedly, it can damage your cooling system. Following are some common reasons for a freeze-up and how to troubleshoot a frozen evaporator coil.

Obstructed Airflow

Inadequate airflow across the evaporator coil is a common cause for a frozen evaporator coil. When the heat-exchange process occurs as intended, the refrigerant expands and turns into a gas. It extracts heat energy from interior air during this conversion, which cools it off. When there’s not enough air blowing across the coil, the refrigerant will struggle to absorb sufficient heat. Its temperature will drop and the coil may freeze. You’ll want to turn off the A/C and allow it to thaw out, and then check for a dirty air filter or dirty evaporator coil. Kinked or otherwise defective ductwork also can reduce airflow.


If your central A/C doesn’t have sufficient refrigerant, this also can freeze the evaporator coil. The refrigerant is still allowed to expand into a gas in the coil, but because there’s not as much of it, the refrigerant will cool more rapidly. This may freeze moisture in the air around the very cold coil. Any problem involving refrigerant should be addressed by a professional.

Unreasonable Demands on Your A/C

If you overwork the A/C – for example, by asking it to cool a home to 65 when it’s 95 degrees outside – this can cause the evaporator coil to freeze up. Avoid this issue by not making unreasonable demands of your A/C.

Mechanical Issues

A variety of mechanical malfunctions can result in the evaporator coil freezing up. Possible problems include a defective blower fan, kinked refrigerant line or clogged filter. Anything that changes pressure in the cooling system can result in the coil freezing up.

If your efforts to troubleshoot a frozen evaporator coil fail to address the problem in your Norther Virginia home, contact Modern Mechanical.