CRST Installation & Maintenance Practices 3 — Questions and Answers
Question 1: A technician discovers a refrigerant leak at a flare fitting during a maintenance visit. What is the correct corrective action?
- Re-tighten the flare nut with a wrench
- Cut off the flare and remake it, then re-tighten (Correct answer)
- Apply refrigerant-rated leak sealant and re-pressurize
- Replace the entire line segment
Correct answer: Cut off the flare and remake it, then re-tighten
Flare fittings that leak are usually deformed; the proper fix is to cut off the old flare and create a new one, then reassemble correctly.
Question 2: What maintenance task should be performed on evaporator coil drain pans to prevent biological growth and drain blockage?
- Apply petroleum jelly to the pan surface
- Add biocide tablets or clean and treat the pan and drain with approved algaecide (Correct answer)
- Spray the pan with CO2 each month
- Insulate the pan to keep it above dew point
Correct answer: Add biocide tablets or clean and treat the pan and drain with approved algaecide
Biocide tablets or algaecide treatments prevent algae, mold, and slime from blocking condensate drains and creating health hazards.
Question 3: During a preventive maintenance visit on a walk-in cooler, the technician measures a high condensing temperature. Which maintenance item is MOST likely the root cause?
- Worn compressor valve plates
- Dirty or blocked condenser coil (Correct answer)
- Low refrigerant charge
- Defective evaporator fan motor
Correct answer: Dirty or blocked condenser coil
A dirty or blocked condenser coil reduces heat rejection, directly raising condensing temperature and system head pressure.
Question 4: What is the correct method for leak-checking a refrigeration system with an electronic leak detector?
- Move the probe rapidly across all joints
- Hold the probe below joints since refrigerant is heavier than air, then move slowly (Correct answer)
- Start at the compressor and work toward the metering device
- Use the detector only on the high-pressure side
Correct answer: Hold the probe below joints since refrigerant is heavier than air, then move slowly
Most refrigerants are heavier than air and collect at low points, so positioning the probe below fittings and moving slowly maximizes detection sensitivity.
Question 5: An evaporator coil is completely encased in ice despite the refrigeration system running. After defrosting, what is the FIRST diagnostic step?
- Add refrigerant charge
- Check airflow across the evaporator for obstructions or failed fans (Correct answer)
- Replace the thermostatic expansion valve
- Increase the defrost cycle frequency immediately
Correct answer: Check airflow across the evaporator for obstructions or failed fans
Restricted airflow is the most common cause of evaporator ice-over and must be verified before assuming a refrigerant or control problem.
Question 6: When replacing a hermetic compressor, why must the system be thoroughly flushed if the previous compressor experienced a burnout?
- To remove excess refrigerant oil from the lines
- To eliminate acid and carbon deposits that remain after a burnout (Correct answer)
- To recalibrate the expansion valve
- To balance refrigerant pressure in the system
Correct answer: To eliminate acid and carbon deposits that remain after a burnout
Acid and carbon contaminants from a compressor burnout remain in the system and will damage a replacement compressor if not removed by flushing and filter-drier replacement.
Question 7: What is the purpose of installing a sight glass with a moisture indicator in a refrigeration liquid line?
- Measure refrigerant flow rate
- Detect refrigerant bubbles indicating undercharge and monitor moisture content (Correct answer)
- Separate oil from refrigerant
- Prevent liquid hammer in the compressor
Correct answer: Detect refrigerant bubbles indicating undercharge and monitor moisture content
A sight glass allows technicians to observe bubbling (indicating undercharge or flash gas) and the color-change indicator alerts them to moisture in the system.
CRST Installation & Maintenance Practices 3
A technician discovers a refrigerant leak at a flare fitting during a maintenance visit.
What is the correct corrective action?