CFC Commercial Refrigeration Systems 5 — Questions and Answers
Question 1: A commercial refrigeration technician is replacing a hermetic compressor. After the repair, the system must be evacuated to at least:
- 500 microns (Correct answer)
- 1000 microns
- 29 inches Hg vacuum
- 0 psig
Correct answer: 500 microns
EPA and industry standards require deep evacuation to 500 microns or lower to ensure all moisture and non-condensable gases are removed before recharging.
Question 2: Which factor most determines the condensing temperature in an air-cooled commercial refrigeration system?
- Refrigerant type used
- Ambient air temperature at the condenser (Correct answer)
- Evaporator coil size
- Compressor displacement
Correct answer: Ambient air temperature at the condenser
In air-cooled systems, the ambient temperature at the condenser sets the lower limit for condensing temperature, as heat must flow from refrigerant to the surrounding air.
Question 3: A technician wants to add refrigerant to a commercial system that uses R-404A. How must this blend be charged?
- As vapor only through the suction service valve
- As liquid only, since it is a near-azeotropic blend (Correct answer)
- As vapor through the liquid line
- As either liquid or vapor without restriction
Correct answer: As liquid only, since it is a near-azeotropic blend
R-404A is a near-azeotropic zeotropic blend; charging as liquid ensures the correct mixture ratio is maintained, since vapor charging can cause fractionation.
Question 4: In a large commercial refrigeration system, a desuperheater is used primarily to:
- Remove superheat from discharge gas to recover heat for water heating (Correct answer)
- Reduce suction gas temperature before the compressor
- Subcool liquid refrigerant in the condenser
- Control evaporator pressure during defrost
Correct answer: Remove superheat from discharge gas to recover heat for water heating
A desuperheater extracts heat from hot discharge gas to heat water, recovering waste heat and improving overall system efficiency.
Question 5: What is the purpose of a crankcase pressure regulator (CPR) valve in a commercial refrigeration system?
- Prevent high discharge pressure during pulldown
- Limit suction pressure to the compressor during high-load pulldown (Correct answer)
- Control refrigerant flow to the evaporator
- Regulate condenser fan speed
Correct answer: Limit suction pressure to the compressor during high-load pulldown
A CPR valve limits the suction pressure entering the compressor during high-load pulldown conditions to prevent motor overload and compressor damage.
Question 6: Which refrigerant safety classification indicates both low toxicity and low flammability, making it commonly used in commercial refrigeration?
- A1 (Correct answer)
- B2L
- A2
- B1
Correct answer: A1
ASHRAE safety class A1 denotes low chronic toxicity (A) and no flame propagation (1), making it the safest class and common in commercial refrigeration applications.
Question 7: A commercial refrigeration system using R-22 needs to be retrofitted. The technician should first:
- Add the new refrigerant on top of the R-22 charge
- Recover all R-22, flush the system, change the oil, then charge with the new refrigerant (Correct answer)
- Vent the R-22 and immediately add the replacement refrigerant
- Mix R-22 with R-410A to create a working blend
Correct answer: Recover all R-22, flush the system, change the oil, then charge with the new refrigerant
A proper R-22 retrofit requires full recovery, system flushing if needed, oil change to compatible POE or AB oil, and then charging with the approved replacement refrigerant.
CFC Commercial Refrigeration Systems 5
A commercial refrigeration technician is replacing a hermetic compressor.
After the repair, the system must be evacuated to at least: