CRST Refrigeration Systems & Components 4 — Questions and Answers
Question 1: What does a high suction superheat combined with normal or low head pressure indicate in a refrigeration system?
- Refrigerant overcharge
- Low refrigerant charge or metering device starving the evaporator (Correct answer)
- Liquid flooding back to the compressor
- Condenser fan motor failure
Correct answer: Low refrigerant charge or metering device starving the evaporator
High superheat with normal or low head pressure points to insufficient refrigerant flow through the evaporator, typically from a low charge or restricted metering device.
Question 2: What is the purpose of a discharge muffler in a reciprocating compressor system?
- Reduce refrigerant velocity to aid oil separation
- Dampen pulsations in the discharge line (Correct answer)
- Cool discharge gas before entering the condenser
- Filter solid particles from discharge vapor
Correct answer: Dampen pulsations in the discharge line
A discharge muffler attenuates pressure pulsations caused by the reciprocating action of the compressor pistons, reducing vibration and noise.
Question 3: When sizing a liquid line, which factor is MOST critical to avoid flash gas formation?
- Line material (copper vs. steel)
- Ensuring adequate subcooling and minimal pressure drop (Correct answer)
- Insulating the liquid line from ambient heat only
- Maximizing line diameter to reduce velocity
Correct answer: Ensuring adequate subcooling and minimal pressure drop
Adequate subcooling provides a safety margin against pressure drop-induced flash gas, which would starve the metering device and reduce capacity.
Question 4: A technician measures compressor amperage at 110% of nameplate rating. What is the most likely cause?
- Low suction pressure
- High head pressure due to condenser fouling or airflow restriction (Correct answer)
- Low refrigerant charge
- Open discharge valve
Correct answer: High head pressure due to condenser fouling or airflow restriction
High head pressure forces the compressor to work harder against greater discharge pressure, drawing excessive amperage.
Question 5: What is the role of a desuperheater in a refrigeration system?
- Remove superheat from suction gas to protect the compressor
- Extract heat from hot discharge gas for water heating (Correct answer)
- Add superheat to liquid refrigerant before the metering device
- Cool the compressor motor windings
Correct answer: Extract heat from hot discharge gas for water heating
A desuperheater is a heat exchanger that recovers heat from superheated discharge gas, commonly used to preheat domestic hot water.
Question 6: Which type of condenser relies solely on natural convection and radiation for heat rejection?
- Evaporative condenser
- Air-cooled condenser with fans
- Static (natural convection) condenser (Correct answer)
- Shell-and-tube water-cooled condenser
Correct answer: Static (natural convection) condenser
A static condenser has no fans or water; it rejects heat through natural air convection and radiation, commonly used in small self-contained units like reach-in coolers.
Question 7: In a cascade refrigeration system, what is the function of the cascade heat exchanger?
- Recover heat from both circuits for space heating
- Act as the condenser for the low-temperature circuit and evaporator for the high-temperature circuit (Correct answer)
- Superheat refrigerant in both circuits simultaneously
- Store refrigerant from both circuits during off cycles
Correct answer: Act as the condenser for the low-temperature circuit and evaporator for the high-temperature circuit
The cascade heat exchanger links two separate refrigerant circuits, rejecting heat from the low-stage condenser into the high-stage evaporator.
CRST Refrigeration Systems & Components 4
What does a high suction superheat combined with normal or low head pressure indicate in a refrigeration system?