CFESA Refrigeration Systems 4 — Questions and Answers
Question 1: What is the primary purpose of a liquid line filter-drier in a commercial refrigeration system?
- Remove moisture and contaminants from the refrigerant (Correct answer)
- Subcool the liquid refrigerant before the metering device
- Increase refrigerant flow velocity to the evaporator
- Separate oil from the refrigerant before the condenser
Correct answer: Remove moisture and contaminants from the refrigerant
A liquid line filter-drier removes moisture, acid, and solid contaminants from the refrigerant to protect the system components.
Question 2: A technician finds frost forming uniformly across the entire evaporator coil in a walk-in cooler. What is the most likely cause?
- Low refrigerant charge
- Defective defrost heater
- Restricted airflow across the coil (Correct answer)
- Overcharge of refrigerant
Correct answer: Restricted airflow across the coil
Uniform frost across the entire evaporator typically indicates restricted airflow, while low charge usually causes frost only on part of the coil.
Question 3: Which refrigerant property is measured by a superheat reading at the evaporator outlet?
- The amount of liquid refrigerant remaining in the evaporator
- The vapor temperature above its saturation point at that pressure (Correct answer)
- The subcooling of refrigerant leaving the condenser
- The enthalpy difference across the compressor
Correct answer: The vapor temperature above its saturation point at that pressure
Superheat is the temperature of refrigerant vapor above its saturation (boiling) temperature at a given pressure, confirming all refrigerant has vaporized.
Question 4: When replacing a hermetic compressor in a commercial reach-in refrigerator, what procedure is MOST critical before brazing the new compressor in place?
- Pressurize the system with nitrogen to 150 psig
- Flush the system with refrigerant to remove air
- Recover all refrigerant and pull a deep vacuum (Correct answer)
- Verify the oil level in the new compressor crankcase
Correct answer: Recover all refrigerant and pull a deep vacuum
All refrigerant must be recovered before opening the system, and a deep vacuum must be pulled to remove moisture and non-condensables before recharging.
Question 5: A commercial ice machine produces small, cloudy ice cubes. What is the MOST likely cause?
- Low water pressure to the machine
- High mineral content in the water supply (Correct answer)
- Refrigerant overcharge in the system
- Faulty harvest temperature sensor
Correct answer: High mineral content in the water supply
High mineral content (hard water) causes cloudy, small ice cubes because minerals become trapped in the ice matrix as water freezes.
Question 6: What does a high discharge pressure combined with a normal or low suction pressure indicate in a commercial refrigeration system?
- Low refrigerant charge
- Dirty or blocked condenser coil (Correct answer)
- Restricted metering device
- Compressor valve failure
Correct answer: Dirty or blocked condenser coil
A dirty condenser reduces heat rejection efficiency, causing discharge pressure to rise while suction pressure remains normal or slightly low.
Question 7: In a commercial refrigeration system using an electronic expansion valve (EEV), which parameter does the controller primarily modulate to maintain proper superheat?
- Compressor speed
- Condenser fan speed
- Valve opening percentage (Correct answer)
- Evaporator fan speed
Correct answer: Valve opening percentage
The EEV controller adjusts the valve opening percentage based on superheat sensor feedback to maintain the target superheat setpoint.
CFESA Refrigeration Systems 4
What is the primary purpose of a liquid line filter-drier in a commercial refrigeration system?