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

Compressor superheat is the temperature of refrigerant vapor above its saturation point at the compressor inlet, ensuring only dry vapor enters to protect the compressor.

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 hermetic compressor encloses the motor and compression mechanism in a welded, gas-tight shell so the motor windings are cooled by refrigerant vapor.

Question 3

What symptom indicates a compressor is short-cycling?

Accepted Answer

The compressor starts and stops frequently in short intervals

Answer

Short-cycling is when the compressor repeatedly starts and stops within short intervals, which can be caused by refrigerant issues, dirty coils, or oversized equipment.

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

A crankcase heater keeps the oil warm during the off cycle to prevent refrigerant from migrating into and mixing with the compressor oil, which could cause damage on startup.

Question 5

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

Accepted Answer

Centrifugal compressor

Answer

Centrifugal compressors are used in large tonnage chillers because they efficiently handle very large volumes of low-pressure refrigerant vapor.

HVAC - Heating, Ventilation, and Air Conditioning Practice Test

HVAC - Heating, Ventilation, and Air Conditioning Practice Test

HVAC Compressors and Condensing Units 2