HVAC Compressors and Condensing Units 2

Question 1

What is 'compressor superheat' and why is it important?

Accepted Answer

The temperature rise of refrigerant vapor above its saturation point before entering the compressor

Answer

Heat added to liquid refrigerant before expansion

Answer

The discharge temperature of refrigerant leaving the compressor

Answer

Heat removed from refrigerant in the condenser

Question 2

What is a hermetic compressor?

Accepted Answer

A compressor where the motor and pump are sealed in a single welded housing

Answer

A compressor with an external belt-drive motor

Answer

A compressor designed only for commercial applications

Answer

A compressor that uses magnetic refrigerant

Question 3

What symptom indicates a compressor is short-cycling?

Accepted Answer

The compressor starts and stops frequently in short intervals

Answer

The compressor runs continuously without shutting off

Answer

The compressor produces a loud grinding noise during operation

Answer

The condenser fan runs but the compressor does not start

Question 4

What is the purpose of a crankcase heater on a compressor?

Accepted Answer

Prevent refrigerant migration into the oil during the off cycle

Answer

Increase compressor efficiency during summer operation

Answer

Heat the refrigerant before it enters the evaporator

Answer

Protect the compressor from low ambient temperatures during operation

Question 5

Which compressor type is most commonly used in large centrifugal chiller applications?

Accepted Answer

Centrifugal compressor

Answer

Reciprocating compressor

Answer

Scroll compressor

Answer

Rotary compressor

Question 6

What causes a compressor to 'trip' on its internal overload protector?

Accepted Answer

Overheating of the motor windings due to excessive current or poor cooling

Answer

Low suction pressure from a clean filter

Answer

Excessive refrigerant subcooling at the condenser outlet

Answer

Low discharge pressure in the system

Question 7

What is 'discharge superheat' in a refrigeration system?

Accepted Answer

The temperature of refrigerant vapor at the compressor outlet above its condensing saturation temperature

Answer

The temperature difference between outdoor air and condensing temperature

Answer

The amount of subcooling at the condenser outlet

Answer

The difference in suction and discharge pressures