313A Refrigerant Handling 2 — Questions and Answers
Question 1: What is the purpose of evacuating a refrigeration system and what vacuum level should be achieved?
- Evacuation removes excess refrigerant; target is 0 psig
- Evacuation removes air and moisture by pulling a deep vacuum; target is 500 microns (0.5 mm Hg) or lower for systems using hygroscopic refrigerants like R-410A (Correct answer)
- Evacuation removes oil; target is atmospheric pressure
- Evacuation is optional if the system is new
Correct answer: Evacuation removes air and moisture by pulling a deep vacuum; target is 500 microns (0.5 mm Hg) or lower for systems using hygroscopic refrigerants like R-410A
Evacuation uses a vacuum pump to remove non-condensable gases (air) and moisture from a refrigeration system. Air reduces efficiency and raises head pressure, while moisture causes acid formation, corrosion, and freeze-ups. A target of 500 microns or lower is standard for R-410A systems, held for at least 15-30 minutes to confirm a tight system.
Question 2: What is the proper method for charging R-410A refrigerant into a system?
- Charge as a gas through the suction side only
- Charge as a liquid through the high side (liquid line) or through the suction side with a metering device to prevent liquid slugging, because R-410A is a near-azeotropic blend (Correct answer)
- Charge as a gas through the discharge side
- Charge by weight through the compressor oil port
Correct answer: Charge as a liquid through the high side (liquid line) or through the suction side with a metering device to prevent liquid slugging, because R-410A is a near-azeotropic blend
R-410A is a near-azeotropic blend (R-32/R-125) that must be charged as a liquid to maintain the correct composition. Liquid can be charged through the liquid line directly or through the suction side using a restrictor to flash the liquid to vapour before it enters the compressor. The cylinder must be inverted or use a dip tube.
Question 3: What is a triple evacuation and when is it recommended?
- Evacuating the system three times in a row
- Three cycles of pulling a vacuum then breaking with dry nitrogen, followed by a final deep vacuum; recommended for systems with significant moisture contamination (Correct answer)
- Three different vacuum pumps used simultaneously
- Evacuating the high side, low side, and oil sump separately
Correct answer: Three cycles of pulling a vacuum then breaking with dry nitrogen, followed by a final deep vacuum; recommended for systems with significant moisture contamination
A triple evacuation involves: (1) pulling a vacuum, (2) breaking the vacuum with dry nitrogen to atmospheric pressure, (3) repeating the vacuum and nitrogen break, and (4) pulling a final deep vacuum to 500 microns or below. The nitrogen sweeps help remove moisture more effectively than a single deep vacuum alone.
Question 4: What are the dangers of mixing different refrigerants in a system?
- It only causes a slight reduction in efficiency
- It can create unpredictable pressures, reduce capacity, damage the compressor, void equipment warranties, and create unsafe operating conditions (Correct answer)
- Different refrigerants naturally separate and cause no issues
- Mixing is recommended for better performance
Correct answer: It can create unpredictable pressures, reduce capacity, damage the compressor, void equipment warranties, and create unsafe operating conditions
Mixing refrigerants creates an unknown blend with unpredictable pressure-temperature characteristics, potentially causing dangerously high pressures, compressor damage from oil compatibility issues, reduced capacity, and voided warranties. Mixed refrigerants cannot be recycled or reclaimed and must be destroyed. This is why recovery cylinders are dedicated to specific refrigerants.
Question 5: What is a standing pressure test and what does it verify?
- A test of the compressor's discharge pressure during operation
- Pressurizing the system with dry nitrogen to a specified pressure and monitoring for a drop over time to verify the system has no leaks (Correct answer)
- A test of the water pressure in cooling towers
- A measurement of oil pressure in the compressor
Correct answer: Pressurizing the system with dry nitrogen to a specified pressure and monitoring for a drop over time to verify the system has no leaks
A standing pressure test involves pressurizing the system with dry nitrogen (often with a trace of refrigerant for electronic leak detection) to the test pressure specified by the equipment manufacturer. The system is then isolated and monitored for a minimum of 24 hours. Any pressure drop indicates a leak that must be found and repaired.
Question 6: Under Canada's Environmental Protection Act, what is the maximum allowable leak rate for commercial refrigeration systems before repairs are required?
- There is no regulated limit
- Systems containing more than a threshold amount of refrigerant must repair leaks within a specified timeframe, and annual leak rates exceeding approximately 10-20% (depending on province) require mandatory reporting and repair (Correct answer)
- 50% per year is acceptable
- Only total loss requires reporting
Correct answer: Systems containing more than a threshold amount of refrigerant must repair leaks within a specified timeframe, and annual leak rates exceeding approximately 10-20% (depending on province) require mandatory reporting and repair
Canadian federal and provincial regulations require operators of commercial and industrial refrigeration systems to track refrigerant usage, repair identified leaks promptly, and report systems exceeding allowable annual leak rates. Specific thresholds vary by province but generally range from 10% to 20% of total charge. Chronic leaking systems may face fines or mandatory replacement.
313A Refrigerant Handling 2
What is the purpose of evacuating a refrigeration system and what vacuum level should be achieved?