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Serving The Greater Fresno Area Since 1970

Serving The Greater Fresno Area Since 1970


Donald P. Dick Air Conditioning Blog

How Central A/C Works

How Central A/C WorksCentral split-system air conditioners have an indoor unit and an outdoor unit. When you hear the term central A/C, the split system is generally the one you’re thinking of. The other main type of central A/C is the package system, which combines its components in one box, usually installed on the roof or a concrete pad next to the house. The main components of the split system central A/C include:


This is contained in the outdoor unit, is cylindrical in shape and normally black in color. It compresses the refrigerant gas and is difficult to check without proper equipment. If your A/C is not cooling but the fan in the outdoor unit is running, it’s possible the compressor has failed.

Condenser (Outdoor Coil)

The condenser, also in the outside unit, has a refrigerant coil fitted with fins. It condenses the hot refrigerant gas into liquid, during which heat energy collected from the home is released into the outside air. It’s important to keep the coil and the fan clear of debris for adequate airflow and heat exchange.

Expansion Valve

This is small and usually found  in the indoor unit and is used to control the expansion of the liquid refrigerant. The expansion reduces the refrigerant temperature down to an operating temperature of approximately 10-15 degrees F. If the valve is faulty, the refrigerant entering the evaporator will not be cold. Sometimes a capillary line is used instead of an expansion valve.

Evaporator (Indoor Coil)

This is inside the air handler, or in many systems connected to the furnace blower, and is similar to the outdoor coil. Air is blown across the cold evaporator coil by the air circulation fan, heat energy removed from the air, and the resulting cool air distributed through ducts into your home. The extracted heat from the air causes the refrigerant liquid to vaporize back into gas before being pumped back outside to the condenser/compressor.


The thermostat controls the A/C by sensing your home’s temperature and switching the A/C on or off. Incorrectly set or faulty thermostats are frequent reasons for poor central A/C performance.

If your central A/C is not working properly, please contact us at Donald P. Dick Air Conditioning. We have been serving the Fresno area for more than 40 years, and our experienced team can service, diagnose, and repair your air conditioning system.

Our goal is to help educate our customers in the greater Fresno, California area about energy and home comfort issues (specific to HVAC systems).  For more information about central A/Cs and other HVAC topics, download our free Home Comfort Resource guide.

Image courtesy of Shutterstock

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