Reasons for High Subcooling in Air Conditioning

A basic air conditioning system has four components: an evaporator, compressor, metering device and condenser. Subcooling is the number of degrees a liquid has been decreased below its boiling temperature. For example, water boils at 212 degrees Fahrenheit; if you decrease the water temperature to 190 degrees, you have subcooled the water 22 degrees. Air conditioners utilize subcooling to remove heat from refrigerants.


A lot of subcooling problems occur in air conditioners because of the type of cooling agent used.

One of the main reasons for high subcooling is the evaporator is clogged or defective and not receiving enough refrigerant. An evaporator in an air conditioning system is the heat exchanger. The warm refrigerant expands and enters the evaporator and is transformed into very cold gas. The warm air enters the evaporator and comes out as cold air, cooling the inside of a car or room. When there is not enough refrigerant entering the evaporator, high subcooling occurs.

Liquid Line

The liquid line is the conduit that connects to the evaporator. If the liquid line is cracked or too small, it prevents enough refrigerant from entering the evaporator and causes high subcooling. A liquid line can also become clogged with debris, preventing refrigerant from entering the evaporator. Without a constant flow of refrigerant through the liquid line and into the evaporator, the air conditioner will not blow out cold air.


A low refrigerant level can also cause high subcooling in the air conditioning unit. The only thing the air conditioner requires, if this is the case, is additional cooling liquid, such as freon. This high subcooling problem is a common occurrence because cooling liquid slowly dissipates under normal operating conditions.


The condenser transforms heat into liquid. When refrigerant backs up into the condenser, high subcooling can occur. Refrigerant can back up into the condenser for many reasons. First, check that the system has enough refrigerant. A bad or damaged condenser will not transform heat into liquid, and replacing the condenser is the only cure for this high subcooling problem. Clogs in the lines, filters or condenser will also cause refrigerant to back up into the condenser.

About the Author

Mitchell Brock has been writing since 1980. His work includes media relations and copywriting technical manuals for Johnson & Johnson, HSBC, FOX and Phillip Morris. Brock graduated from the University of Southern California in 1980, earning a Bachelor of Arts in English.