CFC Commercial Refrigeration Systems 3 — Questions and Answers
Question 1: In a commercial display case, what is the primary function of the anti-sweat heaters on door frames?
- Heat product inside the case
- Prevent condensation on door frames and gaskets (Correct answer)
- Defrost evaporator coils
- Maintain compressor oil temperature
Correct answer: Prevent condensation on door frames and gaskets
Anti-sweat heaters warm door frames and glass edges above the dew point to prevent condensation that would obstruct customer view and cause corrosion.
Question 2: What refrigerant charge condition is indicated when both suction and discharge pressures are lower than normal in a commercial system?
- System overcharged
- Non-condensable gases present
- System undercharged or low refrigerant (Correct answer)
- Compressor valve failure
Correct answer: System undercharged or low refrigerant
Low refrigerant charge reduces mass flow rate, causing both suction and discharge pressures to fall below normal operating levels.
Question 3: Which type of defrost cycle is most energy-efficient for commercial refrigeration cases operating near freezing temperatures?
- Hot gas defrost
- Electric resistance defrost
- Off-cycle defrost (Correct answer)
- Water defrost
Correct answer: Off-cycle defrost
Off-cycle defrost simply stops the refrigeration cycle and allows ambient heat to melt frost, consuming no additional energy compared to electric or hot gas methods.
Question 4: A technician finds oil logging in the evaporator of a commercial refrigeration system. What is the most likely cause?
- Refrigerant overcharge
- Insufficient refrigerant velocity to carry oil back to compressor (Correct answer)
- Excessive superheat setting
- Condenser fan motor failure
Correct answer: Insufficient refrigerant velocity to carry oil back to compressor
Oil logging occurs when refrigerant velocity is too low to entrain oil and return it to the compressor, often from oversized piping or low load conditions.
Question 5: In commercial refrigeration, a thermostatic expansion valve (TXV) bulb should be mounted on the suction line:
- After any horizontal runs, on a vertical riser
- At the 4 or 8 o'clock position on a horizontal suction line (Correct answer)
- Directly on top of the suction line
- After the evaporator outlet, past the accumulator
Correct answer: At the 4 or 8 o'clock position on a horizontal suction line
Mounting the TXV sensing bulb at the 4 or 8 o'clock position on a horizontal suction line ensures it senses refrigerant temperature accurately without being affected by oil pooling at the bottom.
Question 6: Which R-22 replacement refrigerant is approved as a drop-in for existing commercial medium-temperature refrigeration systems without changing the oil?
- R-410A
- R-407C (Correct answer)
- R-134a
- R-404A
Correct answer: R-407C
R-407C has thermodynamic properties similar to R-22 and is compatible with existing mineral oil or alkylbenzene oil, making it suitable for retrofit applications.
Question 7: What is the purpose of a suction-line accumulator in a commercial refrigeration system?
- Store excess refrigerant charge
- Prevent liquid refrigerant slugs from reaching the compressor (Correct answer)
- Subcool liquid refrigerant before the metering device
- Separate refrigerant from non-condensable gases
Correct answer: Prevent liquid refrigerant slugs from reaching the compressor
A suction-line accumulator catches liquid refrigerant before it reaches the compressor, protecting it from hydraulic damage during flood-back conditions.
CFC Commercial Refrigeration Systems 3
In a commercial display case, what is the primary function of the anti-sweat heaters on door frames?