R-12 Receiver/Dryer

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Fig 1: Identifying R-12 Receiver/Dryer

Courtesy of BMW OF NORTH AMERICA, INC.

From the condenser, liquid refrigerant under high pressure flows to the receiver/dryer. The receiver/dryer consists of a cylindrical tank to hold the refrigerant and a solid dryer (comprised of a desiccant such as silica gel, for an R-12 system, or zeolite, for an R-134a system; molecular sieves; and aluminum oxides). The receiver/dryer is designed to separate refrigerant vapor from liquid, so that only liquid is fed to the expansion valve.

The liquid refrigerant enters the tank on the side and flows downward through the solid dryer. Contamination is filtered out by the screen. The dryer absorbs moisture, dirt and acid. However, the dryer element can only absorb a small amount of moisture (6-10 grams for an R-12 system; and 10-16 grams for an R-134a system). Early receiver/dryers have two pressure switches, a high-pressure cutoff switch and a low-pressure cutoff switch. Later receiver/dryers have a combination high/low cutoff switch. These switches interrupt power to the compressor clutch when pressure in the refrigerant circuit is too low or too high.

R-134a receiver/dryers are now used to replace R-12 receiver/dryers.