RSES Installation, Maintenance & Repair Procedures 4 — Questions and Answers
Question 1: A walk-in cooler compressor short-cycles on the high-pressure cutout. Condenser coil is clean and airflow is adequate. What should the technician check next?
- Suction line insulation integrity
- Refrigerant overcharge (Correct answer)
- Low ambient thermostat setting
- Evaporator fan motor amperage
Correct answer: Refrigerant overcharge
If the condenser is clean and airflow is adequate but high pressure is still tripping, refrigerant overcharge is the next likely cause, as excess refrigerant raises condensing pressure.
Question 2: When installing a liquid line solenoid valve, what is the correct orientation requirement?
- Horizontal with the coil facing up
- Vertical with the flow upward
- Any orientation as long as the coil is accessible
- The body must be installed with the flow direction arrow matching refrigerant flow (Correct answer)
Correct answer: The body must be installed with the flow direction arrow matching refrigerant flow
Solenoid valves have a directional flow arrow on the body that must align with the direction of refrigerant flow; incorrect orientation prevents proper valve seating and operation.
Question 3: What is the primary reason nitrogen is used to pressurize a refrigeration system during a leak test rather than oxygen?
- Nitrogen is cheaper than oxygen
- Oxygen can react violently with refrigerant oil creating a combustion risk (Correct answer)
- Nitrogen provides a more accurate pressure reading
- Oxygen dissolves into the refrigerant affecting system capacity
Correct answer: Oxygen can react violently with refrigerant oil creating a combustion risk
Oxygen can react with compressor oil at high pressure to create a potentially explosive mixture, making it extremely dangerous to use in refrigeration systems.
Question 4: A technician installs a new evaporator coil and finds that the refrigerant distributor tubes are different lengths to various coil circuits. Why?
- Longer tubes are used for the lower circuits to compensate for gravity effects
- Different tube lengths compensate for unequal pressure drops to balance refrigerant distribution (Correct answer)
- Longer tubes reduce refrigerant velocity to prevent noise
- Tube length is random and does not affect performance
Correct answer: Different tube lengths compensate for unequal pressure drops to balance refrigerant distribution
Unequal distributor tube lengths are intentional engineering to create equal pressure drops across all coil circuits, ensuring balanced refrigerant distribution and uniform coil performance.
Question 5: During a preventive maintenance visit on a large commercial refrigeration system, what is the correct procedure for checking compressor valve performance?
- Remove the cylinder heads and visually inspect valve reeds annually
- Perform a pump-down test and measure the rate of pressure rise on the low side after shutdown (Correct answer)
- Check motor winding resistance to infer valve condition
- Measure discharge temperature and compare to design specifications
Correct answer: Perform a pump-down test and measure the rate of pressure rise on the low side after shutdown
A pump-down test followed by monitoring the low-side pressure rise rate after compressor shutdown reveals leaking suction or discharge valves without disassembly.
Question 6: When sizing a suction line riser for a refrigeration system with capacity control, what additional design consideration is required?
- The riser must be sized for maximum load only
- A double riser or P-trap may be needed to ensure oil return at reduced load conditions (Correct answer)
- Insulation thickness must increase proportionally with riser height
- A check valve must be installed at the top of every riser
Correct answer: A double riser or P-trap may be needed to ensure oil return at reduced load conditions
Capacity-controlled systems may have insufficient refrigerant velocity at reduced loads to carry oil up a suction riser, requiring a double riser or P-trap arrangement to maintain oil return.
Question 7: A technician is replacing a burned-out compressor motor in a semi-hermetic compressor. What additional service step is mandatory due to the burn contamination?
- Replace only the filter-drier and flush with refrigerant
- Install a suction filter, replace the liquid line filter-drier, and perform an acid test after initial operation (Correct answer)
- Evacuate to 500 microns and recharge with new refrigerant only
- Replace the TXV bulb due to thermal contamination
Correct answer: Install a suction filter, replace the liquid line filter-drier, and perform an acid test after initial operation
A burned compressor leaves acid and carbon contaminants in the system; a suction filter and liquid line drier must be installed and the system acid-tested after initial run to verify cleanup.
RSES Installation, Maintenance & Repair Procedures 4
A walk-in cooler compressor short-cycles on the high-pressure cutout.
Condenser coil is clean and airflow is adequate.
What should the technician check next?