Refrigeration Systems & Components Flashcards

A scroll compressor differs from a reciprocating compressor in that it:

Answer: Compresses refrigerant using two interleaved spiral scrolls without suction valves

Scroll compressors use one fixed and one orbiting spiral scroll to progressively compress refrigerant pockets toward the center discharge port, eliminating the need for suction valves and reducing noise and vibration.

Which compressor type is most commonly used in large commercial refrigeration systems requiring capacity modulation through cylinder unloading?

Answer: Semi-hermetic reciprocating compressor

Semi-hermetic reciprocating compressors are widely used in commercial refrigeration because they allow cylinder unloaders to be installed, enabling staged capacity reduction without stopping the compressor.

Oil logging in an evaporator coil is most likely caused by:

Answer: Insufficient refrigerant velocity to carry oil through the coil back to the compressor

If refrigerant velocity in the evaporator is too low, oil cannot be carried through the coil and returns to the compressor, reducing heat transfer efficiency and starving the compressor of lubrication.

When a hermetic compressor is found to have a grounded motor winding, the refrigerant and oil in the system are likely to be:

Answer: Contaminated with acidic byproducts from the burned winding insulation

A motor burnout releases acidic decomposition products (hydrofluoric and hydrochloric acid) into the refrigerant and oil, requiring an acid cleanup procedure including filter-drier replacement and oil flushing.

A refrigeration technician notices a compressor is short-cycling on the low-pressure cutout. Which of the following is the MOST likely cause?

Answer: Low refrigerant charge or a restricted liquid line filter-drier

Low refrigerant charge or a plugged filter-drier starves the evaporator, causing suction pressure to drop below the low-pressure cutout setpoint and cycling the compressor off prematurely.

What is the function of a crankcase heater on a refrigeration compressor?

Answer: To prevent refrigerant migration into the compressor oil during the off cycle

Crankcase heaters keep the oil warm during the off cycle, preventing refrigerant from migrating into and dissolving in the crankcase oil, which would cause oil foaming and inadequate lubrication at startup.

In a two-stage refrigeration system, an intercooler between the low-stage and high-stage compressors is used to:

Answer: Desuperheat and partially cool the gas between compression stages to improve efficiency

The intercooler removes heat of compression from the low-stage discharge gas before it enters the high-stage compressor, reducing the work of the second stage and improving overall system COP.