313A Refrigerant Handling 2

Question 1

What is the purpose of evacuating a refrigeration system and what vacuum level should be achieved?

Accepted 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

Answer

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?

Accepted 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

Answer

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?

Accepted 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

Answer

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?

Accepted Answer

It can create unpredictable pressures, reduce capacity, damage the compressor, void equipment warranties, and create unsafe operating conditions

Answer

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?

Accepted 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

Answer

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.

Red Seal HVAC 313A Practice Test

Red Seal HVAC 313A Practice Test

313A Refrigerant Handling 2