CRST Installation & Maintenance Practices 2 — Questions and Answers
Question 1: When installing a condensing unit outdoors, what minimum clearance is typically required on the air discharge side?
- 6 inches
- 12 inches
- 24 inches (Correct answer)
- 48 inches
Correct answer: 24 inches
Most manufacturers require at least 24 inches of clearance on the discharge side to prevent recirculation of hot condenser air.
Question 2: Which refrigerant line on a split system should be insulated to prevent condensation and heat gain?
- Liquid line only
- Discharge line only
- Suction line only (Correct answer)
- Both suction and discharge lines
Correct answer: Suction line only
The suction line carries low-pressure, low-temperature refrigerant vapor and must be insulated to prevent heat gain and condensation.
Question 3: What is the purpose of a crankcase heater on a refrigeration compressor?
- Warm refrigerant in the accumulator
- Prevent refrigerant migration into compressor oil during off cycles (Correct answer)
- Increase discharge superheat
- Reduce compressor start current
Correct answer: Prevent refrigerant migration into compressor oil during off cycles
Crankcase heaters keep the oil warm to prevent refrigerant from migrating and diluting the compressor lubricant during the off cycle.
Question 4: A technician is installing copper refrigerant tubing and needs to make a brazed joint. What gas should be used to purge the line during brazing?
- Compressed air
- Oxygen
- Dry nitrogen (Correct answer)
- Carbon dioxide
Correct answer: Dry nitrogen
Dry nitrogen purging during brazing prevents internal oxidation scale that can clog metering devices and damage compressor valves.
Question 5: After installing a new refrigeration system, what is the recommended procedure before charging with refrigerant?
- Charge with refrigerant immediately and check for leaks
- Pressure test with refrigerant at low pressure, then evacuate
- Evacuate to 500 microns, then pressure test with nitrogen, then re-evacuate
- Pressure test with nitrogen, then evacuate to 500 microns or below (Correct answer)
Correct answer: Pressure test with nitrogen, then evacuate to 500 microns or below
The system should be pressure tested with dry nitrogen to check for leaks, then evacuated to 500 microns or lower to remove air and moisture before charging.
Question 6: Which type of filter-drier core is recommended for systems using POE (polyolester) oil?
- Activated alumina core
- Silica gel core
- Molecular sieve core (Correct answer)
- Charcoal core
Correct answer: Molecular sieve core
Molecular sieve desiccant cores are preferred with POE oil systems because they do not react adversely with the highly hygroscopic ester oil.
Question 7: When mounting a remote condenser on a rooftop, which installation requirement is most critical for proper oil return?
- Slope the liquid line upward toward the evaporator
- Install a suction line accumulator at the condenser
- Pitch refrigerant lines toward the compressor and install traps on long vertical risers (Correct answer)
- Use only hard-drawn copper tubing for all line sets
Correct answer: Pitch refrigerant lines toward the compressor and install traps on long vertical risers
Proper pitch and oil traps on vertical suction risers ensure oil entrained in refrigerant vapor is carried back to the compressor.
CRST Installation & Maintenance Practices 2
When installing a condensing unit outdoors, what minimum clearance is typically required on the air discharge side?