ATP Refrigeration Systems & Components 3

Question 1

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

Accepted Answer

Compresses refrigerant using two interleaved spiral scrolls without suction valves

Answer

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.

Question 2

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

Accepted Answer

Semi-hermetic reciprocating compressor

Answer

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.

Question 3

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

Accepted Answer

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

Answer

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.

Question 4

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

Accepted Answer

Contaminated with acidic byproducts from the burned winding insulation

Answer

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.

Question 5

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

Accepted Answer

Low refrigerant charge or a restricted liquid line filter-drier

Answer

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.

(ATP) Accredited Tier Professional Certification (Cooling & Refrigeration) Practice Test

(ATP) Accredited Tier Professional Certification (Cooling & Refrigeration) Practice Test

ATP Refrigeration Systems & Components 3