Refrigerant is the staple of the HVACR industry. Its very existence is the reason we go to work day in and day out. It runs through machinery and systems to cool commercial property, schools, and homes. It keeps food frozen and beverages cold. An accomplished knowledge of how refrigerant cools and how it interacts with system components is a fundamental building block for the HVACR technician. Today we will examine the components and parts of a residential split system.

In The Condenser

Compressor- The heart of the system, the compressor takes low-temperature, low-pressure refrigerant vapor from the evaporator, compresses it, and turns it into a higher temperature and pressure vapor. The refrigerant is now ready for its trip to the condenser coils.

Condenser coils - The part of the system where heat is rejected. Hot, compressed refrigerant vapor from the compressor enters the condenser, circulates through the finned tubing, gives off heat, and turns into liquid refrigerant.

Condenser fan motor assembly - This assembly consists of a fan motor and blade. As the motor rotates, the blade draws air across the condenser coils, cooling and condensing the hot refrigerant vapor to liquid.

Contactor - The contactor accepts an electrical signal from the thermostat and energizes the condenser fan motor and compressor.

Capacitors - Capacitors are used to assist compressor and condenser fan motors to start and run.

Crankcase heater - Typically fit as a band around the compressor, the crankcase heater applies heat to the compressor, preventing the migration of refrigerant to the compressor's oil.

Low-pressure switch - In our residential application, the low-pressure switch prevents the system from running in a low refrigerant condition.

High-pressure switch - This switch prevents the system from running during excessive high-side or head pressure caused by conditions such as a dirty condenser coil or defective fan motor.

Service valves - These valves allow for isolation or access into the refrigerant side of the system.

Low-ambient control - This control comes in two versions; one cycles the condenser fan on and off, and the other modulates the condenser fan speed. In both cases, the aim is to keep the head pressure elevated during cooler outside temperatures.

Refrigerant Lines

Suction line- The suction line carries superheated cool refrigerant vapor to the compressor. The suction line is insulated to prevent exterior condensation and refrigerant vapor temperature loss.

Discharge line - The discharge line carries superheated hot refrigerant vapor to the condenser.

Liquid line - The liquid line carries warm, subcooled refrigerant liquid to the evaporator metering device.

More Components

Evaporator- The system component that absorbs heat from inside the dwelling. The evaporator takes a mixture of vapor and liquid refrigerant from the metering device and uses the heat load from the dwelling to boil it into a saturated vapor. The vapor becomes superheated as more heat is added beyond the state of saturation. This vapor continues on in the suction line to the compressor.

Metering device - Usually found in residential applications as either a thermal expansion valve, capillary tube, or fixed orifice type, the metering device takes warm, subcooled, high-pressure liquid from the condenser and feeds it to the evaporator.

Solenoid valve - Automatically controls the flow of liquid refrigerant to the metering device.

Liquid line filter drier - The filter drier removes dirt, moisture, and acids from the refrigerant circuit. This drier is usually located in the liquid line before the moisture and liquid sight glass.

Moisture and liquid sight glass - The sight glass indicates moisture and the level of liquid refrigerant in the liquid line. The sight glass is located just before the metering device in the liquid line.

Keys To Success

Successful technicians know where in the system refrigerant is supposed to be in a vapor or liquid state. They also know if it is supposed to be saturated, superheated, or subcooled at any given point in the system. Two excellent resources for further study areRefrigeration & Air Conditioning Technology, 4th edition, published by Delmar Publishing, andModern Refrigeration and Air Conditioning, published by the Goodheart-Willcox Co.

David E. Rothacker is a member of the National Comfort Institute's Advisory Board and a National Comfort Team Founding Member. For questions or comments on Tech Basics, contact Rothacker at

Publication date: 07/26/2004