Compressors and Condensing Units Flashcards
7 cards from real HVAC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Compressors and Condensing Units flashcards as text
What is 'compressor superheat' and why is it important?
Answer: The temperature rise of refrigerant vapor above its saturation point before entering the compressor
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.
What is a hermetic compressor?
Answer: A compressor where the motor and pump are sealed in a single welded housing
A hermetic compressor encloses the motor and compression mechanism in a welded, gas-tight shell so the motor windings are cooled by refrigerant vapor.
What symptom indicates a compressor is short-cycling?
Answer: The compressor starts and stops frequently in short intervals
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.
What is the purpose of a crankcase heater on a compressor?
Answer: Prevent refrigerant migration into the oil during the off cycle
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.
Which compressor type is most commonly used in large centrifugal chiller applications?
Answer: Centrifugal compressor
Centrifugal compressors are used in large tonnage chillers because they efficiently handle very large volumes of low-pressure refrigerant vapor.
What causes a compressor to 'trip' on its internal overload protector?
Answer: Overheating of the motor windings due to excessive current or poor cooling
The internal overload protector opens when motor windings overheat from excessive amperage draw or insufficient refrigerant cooling of the motor.
What is 'discharge superheat' in a refrigeration system?
Answer: The temperature of refrigerant vapor at the compressor outlet above its condensing saturation temperature
Discharge superheat is measured at the compressor outlet and indicates the temperature of discharge gas above its saturation point at the discharge pressure.