CRST Refrigeration Systems & Components 3 — Questions and Answers
Question 1: What condition is indicated when frost forms uniformly across the entire evaporator coil?
- Refrigerant overcharge
- Normal operation with adequate airflow (Correct answer)
- Low refrigerant charge causing early evaporation
- Restricted metering device causing low superheat
Correct answer: Normal operation with adequate airflow
Uniform frost across the full coil typically indicates normal operation with proper refrigerant flow and adequate airflow.
Question 2: A brazed-plate heat exchanger used as an evaporator offers which advantage over a shell-and-tube evaporator?
- Easier to clean internally
- Higher refrigerant charge requirement
- Compact size with high heat transfer efficiency (Correct answer)
- Better suited for flooded operation only
Correct answer: Compact size with high heat transfer efficiency
Brazed-plate heat exchangers provide very high surface area-to-volume ratios, offering superior heat transfer in a compact package.
Question 3: What is the effect of non-condensable gases on condenser performance?
- They lower condensing pressure
- They raise condensing pressure and reduce efficiency (Correct answer)
- They have no effect on head pressure
- They improve heat transfer by mixing with refrigerant
Correct answer: They raise condensing pressure and reduce efficiency
Non-condensable gases (air, nitrogen) blanket condenser tubes, raising head pressure and reducing heat transfer efficiency.
Question 4: A scroll compressor produces a rattling noise on startup. What is the most likely cause?
- Liquid refrigerant in the suction line
- Worn scroll wraps due to normal aging
- Reverse rotation of the compressor (Correct answer)
- Clogged discharge muffler
Correct answer: Reverse rotation of the compressor
Scroll compressors are rotation-sensitive; reverse rotation causes the scrolls to separate and produces a characteristic rattling or grinding noise.
Question 5: What is the function of a hot gas bypass valve in a refrigeration system?
- Recover discharge heat for defrost
- Maintain minimum evaporator pressure during light loads (Correct answer)
- Prevent high head pressure during summer
- Bypass refrigerant around the condenser
Correct answer: Maintain minimum evaporator pressure during light loads
A hot gas bypass valve routes hot discharge gas to the low side to maintain minimum evaporator pressure and prevent coil freeze-up at light loads.
Question 6: Which component in a refrigeration system is specifically designed to separate oil from refrigerant vapor on the high-pressure side?
- Suction accumulator
- Oil separator (Correct answer)
- Filter-drier
- Desuperheater
Correct answer: Oil separator
An oil separator is installed in the discharge line to capture oil before it enters the condenser, returning it directly to the compressor crankcase.
Question 7: In a parallel rack refrigeration system used in supermarkets, what is the main advantage over individual compressor systems?
- Simpler controls and wiring
- Redundancy and shared capacity allowing better load management (Correct answer)
- Lower refrigerant charge per circuit
- Elimination of suction line piping
Correct answer: Redundancy and shared capacity allowing better load management
Parallel rack systems allow multiple compressors to share load, providing redundancy so that one compressor failure does not shut down the entire system.
CRST Refrigeration Systems & Components 3
What condition is indicated when frost forms uniformly across the entire evaporator coil?