Substitute refrigerants & oils: EPA 608 Practice Questions

R-410A is a blend of which two refrigerants?

R-410A is a near-azeotropic blend of R-32 and R-125. R-454B is R-32 with R-1234yf, and R-502 contained R-22 and R-115.

What is temperature glide?

The components of a zeotropic blend boil at different temperatures, so at a constant pressure the blend's saturation temperature changes during evaporation or condensation.

Why should a zeotropic blend such as R-407C be charged from the cylinder as a liquid?

The components evaporate at different rates, so drawing vapor removes more of the lighter component (fractionation). Removing liquid keeps the composition correct.

Which refrigerant is an azeotropic blend that behaves like a single substance?

500-series blends such as R-507A are azeotropes with no meaningful glide. 400-series blends such as R-407C, R-454B and R-404A are zeotropic.

Which lubricant is most commonly used with HFC refrigerants such as R-410A and R-32 in stationary equipment?

HFCs do not mix well with mineral oil, so POE (and in some equipment PVE) oil is used to keep oil returning to the compressor.

Why must POE oil containers be kept tightly sealed?

POE oil is hygroscopic: it pulls moisture from the air quickly, and moisture in a system causes acids and sludge. Open only what you need and reseal at once.

Mineral oil was the traditional lubricant for which refrigerants?

Mineral oil mixes well with chlorine-containing CFCs and HCFCs. With HFCs it separates and may not return to the compressor.

Which lubricant is typically used in vehicle air conditioning systems charged with R-1234yf or R-134a?

Automotive compressors mainly use PAG oil (some electric compressors use POE). PAG is also very hygroscopic.

What is the problem with putting two different refrigerants into the same recovery cylinder?

Reclaimers cannot separate most mixtures back to AHRI 700 purity, so mixed refrigerant is often refused or must be destroyed at a high cost. Keep one refrigerant per cylinder.

R-454B is a blend of which refrigerants?

R-454B is roughly 69% R-32 and 31% R-1234yf by weight, which gives it a much lower GWP than R-410A.

R-1234yf belongs to which refrigerant family?

R-1234yf is an HFO: it contains no chlorine (zero ODP) and breaks down quickly in the atmosphere, giving it a very low GWP.

What are R-290 and R-600a?

R-290 is propane and R-600a is isobutane. Both are hydrocarbon refrigerants with zero ODP, very low GWP and A3 (higher flammability) safety class.

A system designed for R-410A is low on charge. May the technician top it off with R-32?

Mixing refrigerants creates an unknown blend and contaminates the charge. Also, R-32 is flammable (A2L), and an A1 system is not designed or listed for a flammable refrigerant.

On a system using a zeotropic blend, which saturation temperature from the PT chart is used to calculate superheat?

Superheat is measured from the dew point (all vapor), and subcooling from the bubble point (all liquid). With a glide, the two values differ.