In this short episode, we review the basics of the refrigerant circuit. The standard HVAC refrigeration circuit has four main components: compressor, condenser, metering device, and evaporator.

The compressor squeezes refrigerant vapor into a smaller volume by applying lots of pressure. It simultaneously moves and compresses gaseous refrigerant. The more a compressor has to compress a gas, the less gas it moves. The more gas a compressor moves, the less gas it compresses. Then, the refrigerant leaves the compressor via the discharge line. The discharge line is very hot because the temperature increases with pressure.

The hot vapor feeds into the top of the condenser. The condenser brings the gaseous refrigerant back down to a liquid. Condensers come in all shapes for various applications, but all condensers' main goal is heat exchange. Condensers desuperheat, fully condense (change vapor to liquid), and subcool. Subcooled liquid refrigerant leaves the bottom of the condenser via the liquid line.

The liquid line leads warm, subcooled liquid refrigerant to the metering device. The metering device's goal is to drop the refrigerant's pressure. That pressure drop facilitates boiling in the evaporator coil.

The evaporator absorbs heat from the space. Fans blow warm air over the coils, allowing that heat to come into contact with the refrigerant. The refrigerant boils when it absorbs enough heat. The last few rows of the evaporator are where superheating occurs. Superheat is the temperature above the saturation point; superheat indicates that the refrigerant is all vapor, no longer a liquid-vapor mix. Then, the vapor refrigerant travels back to the compressor via the suction line; the refrigerant circuit restarts. The suction line is rather cool; we use some of that cool refrigerant gas to cool down the compressor.

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