Refrigerants and Lubricants
Refrigerants and Lubricants
This domain tests refrigerant safety classifications, blend behavior, lubricant compatibility, and service practices that prevent contamination. Questions often combine a refrigerant property with a field procedure.
Core rules
- HCFC-22 is phased out in new equipment; HFCs such as R-410A and R-134a remain common, while A2L refrigerants (for example R-32 and R-454B) have mild flammability and require ignition-source controls.
- R-410A is a zeotropic blend with glide. Charge it as liquid from the cylinder; vapor charging can fractionate the blend and change composition.
- Use dew-point saturation temperature for superheat and bubble-point for subcooling when a blend has glide.
- Mineral oil is not suitable for HFC systems; POE and PVE lubricants are used. POE is hygroscopic, so keep containers sealed and minimize exposure.
- Never mix lubricants or top off a POE system with mineral oil. Retrofit procedures require a documented flush, new filter drier, and manufacturer approval.
Worked example
A technician finds a leaking R-410A system and repairs the leak. The nameplate charge is 8 lb. After evacuation, the technician charges 8 lb as liquid by weight, then checks subcooling against the bubble-point temperature. The reasoning: weight is the most accurate method, and liquid charging preserves blend composition. If only 7.2 lb were added and the technician "topped off" with vapor, the remaining blend could be fractionated, making superheat and performance unpredictable.
Traps
Assuming all HFCs use mineral oil; using the midpoint of glide for both superheat and subcooling; charging a zeotropic blend as vapor; and leaving POE oil open to air. Also, A2L flammability does not mean the refrigerant is harmless-charge limits and ignition controls still apply.