reverses until the contacts are separated at a pre-determined low-suction pressure, thus breaking the motor controller circuit and stopping the compressor.

SUCTION LINE FILTER-DRIER. - Some systems include a low-side filter-drier (fig. 6-31) at the compressor end of the suction line. The filter-drier used in the suction line should offer little resistance to flow of the vaporized refrigerant, as the pressure difference between the pressure in the evaporator and the inlet of the compressor should be small. These filter-driers function to remove dirt, scale, and moisture from the refrigerant before it enters the compressor.

GAUGES AND THERMOMETERS. - Between the suction line stop valve and the compressor, a pressure gauge and thermometer may be provided to show the suction conditions at which the compressor is operating. The thermometer shows a higher temperature than the temperature corresponding to the suction pressure indicated on the gauge, because the refrigerant vapor is superheated during its passage from the evaporator to the compressor.

ACCUMULATORS AND OIL SEPARATORS. - Liquid refrigerant must never be allowed to enter the compressor. Liquids are noncompressible; in other words, their volume remains the same when compressed. An accumulator (fig. 6-32) is a small tank accessory; that is, a safety device designed to prevent liquid refrigerant from flowing into the suction line and into the compressor. A typical accumulator has an

Figure 6-30. - Pressure type cut-in, cutout control switch.

Figure 6-31. - A suction line filter-drier.

outlet at the top. Any liquid refrigerant that flows into the accumulator is evaporated, and then the vapor will flow into the suction line to the compressor.

Oil from the compressor must not move into the rest of the refrigeration system. Oil in the lines and evaporator reduces the efficiency of the system. An oil separator (fig. 6-33) is located between the compressor discharge and the inlet of the condenser. The oil separator consists of a tank or cylinder with a series of baffles and screens, which collect the oil. This oil settles to the bottom of the separator. A float arrangement operates a needle valve, which opens a return line to the compressor crankcase.

Q7. What are the three types of compressors used in refrigeration systems?

Q8. What is the difference between the internal and external bellows crankshaft seal?

Q9. What are the two drawbacks of a hermetic compressor?

Q10. What are the two primary types of evaporators?

Q11. A capillary tube-metering device is most commonly used on what type of refrigeration equipment?

Q12. What is the function of a sight-flow indicator?

REFRIGERANTS

Learning Objective: Understand and identify classification of common refrigerants and their application. Understand the requirements for ozone protection and the Clean Air Act.

Figure 6-32. - Accumulator location.