Commercial Refrigeration FINAL TEST
2026/2027 Questions and Answers
(Graded A+)
How is the cooling effect in a mechanical refrigeration system produced? - ANSWER -
Evaporation of liquid refrigerant into vapor
What is the primary purpose of a compressor? - ANSWER - It circulates and pressurizes the
refrigerant vapor before the vapor Is condensed for re use
Name another function that must be performed by the compressor - ANSWER - Is raise the
pressure and temperature of the refrigerant vapor. This allows the refrigerant to condense into a
liquid as it circulates through the condenser
What characteristic defines an "open" type compressor? - ANSWER - Has a drive shaft
protruding from the compressor
What are the two main disadvantages of a hermetic compressor? - ANSWER - If either the
motor or compressor malfunctions, the entire unit must be replaced. The motor is actually a part
of the refrigerant circulation system. This means that a burnout can contaminate the entire
system
In a reciprocating compressor, the piston is connected to the crankshaft by a _____ - ANSWER
- Connecting rod
Name the three elements of performance that are the major factors in evaluating a compressor -
ANSWER - Efficiency, capacity, and economy of operation
If the suction gas superheat is too low, What could be the result? - ANSWER - Liquid refrigerant
might enter the compressor. This causes stress on the compressor valves, wrist pins, rods,
shaft, etc. It also causes excessive foaming of the oil in the crankcase and other damaging
effects. The compressor will not reach its rated capacity
, What will happen if the suction gas temperature is too high? - ANSWER - Will cause the
compressor to run hot
What purpose do the fins attached to the condenser tubes serve? - ANSWER - Increase the
surface area for heat transfer
What is the purpose of subcooling? - ANSWER - To prevent the liquid from vaporizing
prematurely
If condensing pressure is higher than the corresponding condensing temperature, what is
normally the cause? - ANSWER - Non condensable gases
How is compressor efficiency often judged? - ANSWER - Btu per cubic foot (Btu/ft^3) of
displacement
When the same model of open type compressor is used with both air cooled and water cooled
condensing units, which is usually run at a slightly higher rpm? - ANSWER - Water cooled
What is the equation for ratio of compression? - ANSWER - The absolute discharge pressure
(psig plus 14.7) divided by the absolute suction pressure (psig plus 14.7)
What type of compressor is found in large applications up to 10000 tons? - ANSWER -
Centrifugal compressors
Which compressor utilizes two helical rotors to compress the refrigerant gas? - ANSWER -
Screw compressor
What is the most outstanding advantage of the hermetically sealed compressor over the open
type? - ANSWER - Has no protruding crankshaft or shaft seal
How are the disadvantages overcome in compressors that are employed in low temperature
applications? - ANSWER - Use supplementary cooling
2026/2027 Questions and Answers
(Graded A+)
How is the cooling effect in a mechanical refrigeration system produced? - ANSWER -
Evaporation of liquid refrigerant into vapor
What is the primary purpose of a compressor? - ANSWER - It circulates and pressurizes the
refrigerant vapor before the vapor Is condensed for re use
Name another function that must be performed by the compressor - ANSWER - Is raise the
pressure and temperature of the refrigerant vapor. This allows the refrigerant to condense into a
liquid as it circulates through the condenser
What characteristic defines an "open" type compressor? - ANSWER - Has a drive shaft
protruding from the compressor
What are the two main disadvantages of a hermetic compressor? - ANSWER - If either the
motor or compressor malfunctions, the entire unit must be replaced. The motor is actually a part
of the refrigerant circulation system. This means that a burnout can contaminate the entire
system
In a reciprocating compressor, the piston is connected to the crankshaft by a _____ - ANSWER
- Connecting rod
Name the three elements of performance that are the major factors in evaluating a compressor -
ANSWER - Efficiency, capacity, and economy of operation
If the suction gas superheat is too low, What could be the result? - ANSWER - Liquid refrigerant
might enter the compressor. This causes stress on the compressor valves, wrist pins, rods,
shaft, etc. It also causes excessive foaming of the oil in the crankcase and other damaging
effects. The compressor will not reach its rated capacity
, What will happen if the suction gas temperature is too high? - ANSWER - Will cause the
compressor to run hot
What purpose do the fins attached to the condenser tubes serve? - ANSWER - Increase the
surface area for heat transfer
What is the purpose of subcooling? - ANSWER - To prevent the liquid from vaporizing
prematurely
If condensing pressure is higher than the corresponding condensing temperature, what is
normally the cause? - ANSWER - Non condensable gases
How is compressor efficiency often judged? - ANSWER - Btu per cubic foot (Btu/ft^3) of
displacement
When the same model of open type compressor is used with both air cooled and water cooled
condensing units, which is usually run at a slightly higher rpm? - ANSWER - Water cooled
What is the equation for ratio of compression? - ANSWER - The absolute discharge pressure
(psig plus 14.7) divided by the absolute suction pressure (psig plus 14.7)
What type of compressor is found in large applications up to 10000 tons? - ANSWER -
Centrifugal compressors
Which compressor utilizes two helical rotors to compress the refrigerant gas? - ANSWER -
Screw compressor
What is the most outstanding advantage of the hermetically sealed compressor over the open
type? - ANSWER - Has no protruding crankshaft or shaft seal
How are the disadvantages overcome in compressors that are employed in low temperature
applications? - ANSWER - Use supplementary cooling
