September 2, 2019

What Causes a Frozen Coil


A frozen coil in your air conditioner or heat pump usually gets noticed once you start getting warm air coming from your registers. There are many things which can cause warm air instead of cold air to filter into your house. This article will look at many common reasons a coil can freeze.

There are two coils in a typical HVAC system: The condenser coil and the evaporator coil. The condenser coil is in the outside condenser unit and the evaporator coil is in the inside evaporator unit. These two units work together to cool the air circulating throughout your home.

A frozen coil must be defrosted before a technician can examine the problem. The system needs to be turned off until it defrosts or you can turn your thermostat from “Auto” or “Cool” setting to fan.

Faulty Thermostat

Thermostat Error

The thermostat can malfunction with it’s sensors and cause an air conditioning system to over work. If the sensor is not letting the system know when the desired temperature is reached, the system will continue to send more and more cool air and overwork the system. An overworked system will not perform well or cool itself properly.

Improper Air Flow, Fan or Fan Motor Failure

Dirty Air Filter

If your system has improper or impeded air flow it can cause your system to overwork and ultimately fail. An overworked system can cause a frozen coil. One of the biggest culprits impeding airflow are dirty filters. Air filters need to be changed at least every three months or every month if you have high traffic or pets. Also make sure that your indoor and outdoor units are free from clutter or debris.

Failed TXV

Faulty Thermo Expansion Valve

The TXV is the Thermal Expansion Valve and it controls the flow of refrigerant. Improper flow of refrigerant can cause a frozen coil.

Condensate Lines, Pump

Candensate Lines

Condensate lines carry condensation (water created from humidity) from the system. Water can collect and freeze if the line is blocked or broken.

The condensate pump facilitates the flow of accumulated condensation through the condensate lines.

Refrigerant Leaks

Often Refrigerant leaks are found in multiples. These leaks cannot always be visually detected and generally require a specialized refrigerant sensor to be found. These leaks can cause a frozen coil. If your system is low on refrigerant, it is leaking out somewhere. Not all coil leaks are repairable and can mean that the coil needs to be replaced.



In conclusion, a frozen coil needs to be inspected by a licensed technician. Tests must be performed in order to ensure that proper measures are taken so your HVAC system does not become more damaged.

The Air Doctor Heating and Air technicians are equipped to find the source of the problem and effect the proper remedy. Our technicians are highly trained and skilled in handling HVAC equipment, repairs, maintenance and installations.


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