CFESA Refrigeration Systems 5 — Questions and Answers
Question 1: A walk-in freezer compressor short-cycles (runs briefly and shuts off repeatedly). The low-pressure cutout is tripping. What is the MOST likely cause?
- Condenser coil is dirty
- Low refrigerant charge (Correct answer)
- Faulty high-pressure switch
- Overcharge of refrigerant
Correct answer: Low refrigerant charge
A low refrigerant charge causes suction pressure to drop below the low-pressure cutout setpoint, causing the compressor to short-cycle on low pressure.
Question 2: Which type of refrigerant leak detection method is BEST suited for identifying the exact location of a small leak in a hard-to-reach area of tubing?
- Electronic leak detector sweep
- Nitrogen pressure test with soap bubbles
- UV dye inspection with black light (Correct answer)
- Refrigerant standing pressure test
Correct answer: UV dye inspection with black light
UV dye previously added to the system glows under UV light, pinpointing the exact leak location even in tight or hidden areas.
Question 3: What is the function of a crankcase pressure regulator (CPR) valve in a commercial refrigeration system?
- Prevent compressor overload during pulldown by limiting suction pressure (Correct answer)
- Regulate discharge pressure during high ambient conditions
- Control refrigerant flow to multiple evaporators
- Maintain head pressure during low ambient temperatures
Correct answer: Prevent compressor overload during pulldown by limiting suction pressure
A CPR valve limits the maximum suction pressure entering the compressor to prevent motor overload during high-load pulldown conditions.
Question 4: A commercial refrigeration condenser fan motor fails. Before replacing it, what should the technician verify about the replacement motor?
- The motor rotation direction matches the original (Correct answer)
- The motor is rated for outdoor use only
- The motor uses the same refrigerant type
- The motor frame size is larger than the original
Correct answer: The motor rotation direction matches the original
Condenser fan motors must rotate in the correct direction to move air properly through the condenser coil; wrong rotation causes inadequate heat rejection.
Question 5: When performing a triple evacuation on a commercial refrigeration system, what gas is used between each vacuum pull to purge moisture?
- Dry nitrogen (Correct answer)
- Carbon dioxide
- Clean refrigerant vapor
- Compressed air
Correct answer: Dry nitrogen
Dry nitrogen (dew point below -60°F) is used to break the vacuum between pulls, absorbing remaining moisture before the next evacuation cycle.
Question 6: A reach-in display case has a warm cabinet temperature but the evaporator fan is running and no ice is visible on the coil. Suction pressure is normal. What should be checked FIRST?
- Refrigerant charge level
- Door gaskets and seals for air infiltration (Correct answer)
- Compressor valve efficiency
- Condenser coil cleanliness
Correct answer: Door gaskets and seals for air infiltration
When the refrigeration system appears to operate normally but cabinet temperature is warm, damaged door gaskets allowing warm air infiltration is the most common cause.
Question 7: What is the purpose of a head pressure control valve (also called a flooding valve) on an air-cooled condenser in cold ambient conditions?
- Prevent liquid refrigerant from flooding back to the compressor
- Maintain minimum condensing pressure by restricting liquid line flow (Correct answer)
- Reduce compressor discharge temperature in summer
- Control refrigerant flow to a remote condenser
Correct answer: Maintain minimum condensing pressure by restricting liquid line flow
In cold weather, a head pressure control valve maintains minimum condensing pressure by partially flooding the condenser with liquid refrigerant to reduce effective coil surface.
CFESA Refrigeration Systems 5
A walk-in freezer compressor short-cycles (runs briefly and shuts off repeatedly).
The low-pressure cutout is tripping.
What is the MOST likely cause?