RSES Installation, Maintenance & Repair Procedures 5 — Questions and Answers
Question 1: When performing a standing pressure test on a newly installed refrigeration system, what is the recommended holding time before declaring the system leak-free?
- 15 minutes at operating pressure
- 24 hours minimum at test pressure (Correct answer)
- 1 hour with electronic leak detector confirmation
- 30 minutes followed by nitrogen purge
Correct answer: 24 hours minimum at test pressure
A minimum 24-hour standing pressure test is recommended to allow temperature stabilization and confirm that pressure remains constant, indicating a leak-free system.
Question 2: During installation of a parallel compressor rack, why are unloaders or capacity steps typically required on individual compressors?
- To prevent compressor overheating during summer operation
- To allow staged capacity matching to varying load conditions and prevent short cycling (Correct answer)
- To reduce electrical starting current below panel capacity
- To synchronize compressor rotation speeds
Correct answer: To allow staged capacity matching to varying load conditions and prevent short cycling
Capacity control via unloaders or staging allows the rack to match refrigeration output to varying load, preventing short cycling and improving efficiency across different operating conditions.
Question 3: A technician finds that a newly commissioned system has high discharge superheat (greater than 75°F above condensing temperature). What is the most likely cause?
- Refrigerant overcharge
- Low evaporator airflow
- Low refrigerant charge or refrigerant restriction (Correct answer)
- Condenser fan cycling on too frequently
Correct answer: Low refrigerant charge or refrigerant restriction
Excessively high discharge superheat typically indicates low refrigerant charge or a restriction starving the compressor of suction vapor, causing gas to superheat more than normal.
Question 4: What is the proper technique for straightening bent condenser or evaporator fins during maintenance?
- Use a flat-blade screwdriver to carefully bend fins back individually
- Use a fin comb sized to match the fins-per-inch rating of the coil (Correct answer)
- Apply moderate heat with a heat gun to relax the aluminum before straightening
- Fins should never be straightened and require coil replacement
Correct answer: Use a fin comb sized to match the fins-per-inch rating of the coil
A fin comb matched to the coil's fins-per-inch count is designed to straighten multiple fins simultaneously without further damage to the delicate coil surface.
Question 5: When installing a refrigeration system in a machinery room, which code requirement governs the minimum ventilation rate?
- ASHRAE Standard 15 specifies ventilation based on refrigerant quantity and room volume (Correct answer)
- NEC Article 440 specifies minimum airflow in CFM per compressor horsepower
- EPA Section 608 specifies ventilation for all refrigerant types
- OSHA 1910.119 specifies ventilation for all refrigerants above 100 lbs
Correct answer: ASHRAE Standard 15 specifies ventilation based on refrigerant quantity and room volume
ASHRAE Standard 15 (Safety Standard for Refrigeration Systems) provides the formula and requirements for machinery room ventilation rates based on refrigerant type and quantity.
Question 6: A technician needs to braze a refrigerant line while it is still pressurized with nitrogen. What is the correct procedure?
- Reduce nitrogen pressure to below 5 PSI and braze normally
- Brazing on a pressurized line is never permitted; the line must be fully evacuated first
- Maintain 2–3 PSIG nitrogen flow through the line while brazing to prevent oxidation scaling (Correct answer)
- Purge nitrogen completely before brazing, then re-pressurize afterward
Correct answer: Maintain 2–3 PSIG nitrogen flow through the line while brazing to prevent oxidation scaling
Industry best practice is to flow dry nitrogen at 2–3 PSIG through the line while brazing to prevent internal oxidation (black scale) that can contaminate the refrigeration system.
Question 7: After completing repairs on a commercial refrigeration system, what is the correct sequence for returning the system to service?
- Charge refrigerant, start compressor, then leak check with system running
- Pressure test with nitrogen, evacuate, charge refrigerant, verify operation, document (Correct answer)
- Evacuate, charge, start compressor, pressure test during first run
- Start compressor dry to verify mechanical operation before charging
Correct answer: Pressure test with nitrogen, evacuate, charge refrigerant, verify operation, document
The correct return-to-service sequence is: leak test with nitrogen, pull deep vacuum, charge with correct refrigerant amount, verify system operation, then document all work performed.
RSES Installation, Maintenance & Repair Procedures 5
When performing a standing pressure test on a newly installed refrigeration system, what is the recommended holding time before declaring the system leak-free?