Substitute refrigerants and oils on the EPA 608 Core

Answer: C. Invert cylinder and use a throttling valve

• AWrong: bypassing the manifold means sending liquid into the suction side with nothing to meter it, which risks slugging the compressor.
• BWrong: heating the cylinder to push vapor out separates the blend's components, and heating cylinders is unsafe.
• CCorrect: draw the blend out as liquid to keep its composition, then meter it into the low side through a throttling valve so it flashes before it reaches the compressor.
• DWrong: charging blends as vapor only can change the composition of what goes into the system; blends are charged as liquid.

Blends often require charging by weight. Liquid charging from an inverted cylinder through a throttling valve prevents fractionation and liquid slugging.

Answer: B. The blend fractionates if charged as a vapor

• AWrong: glide means pressure and temperature don't line up the way they do for a single refrigerant; it doesn't remove pressure differences.
• BCorrect: the components boil at different temperatures, so vapor charging takes out more of the volatile components; charge zeotropic blends as liquid.
• CWrong: oil choice has nothing to do with glide, and most HFC blends call for POE oil rather than mineral oil.
• DWrong: zeotropic components condense and boil over a temperature range, not all at once; that is what glide means.

Zeotropic blends exhibit temperature glide, meaning their individual components boil at different temperatures. To prevent fractionation, they must be charged as a liquid rather than a vapor.

Answer: C. Comparative risk assessment including environmental impact, safety, and health effects

• AWrong: GWP is one of the factors SNAP weighs, but it isn't the only one.
• BWrong: chemical makeup alone doesn't settle acceptability; SNAP looks at how the substitute behaves in a given end use.
• CCorrect: SNAP compares a substitute's overall risk, including ozone depletion, global warming, flammability, toxicity and exposure, against the other options for that end use.
• DWrong: cost is not a SNAP criterion; the program reviews risks to health and the environment.

Under the SNAP program, a refrigerant's acceptability is determined by comparative risk assessment that evaluates its ozone depletion potential, global warming potential, flammability, toxicity, exposure potential, and environmental fate compared to other substitutes.

Answer: D. The remaining blend components have altered from their original formulation.

• AWrong: glide doesn't flood the compressor; the problem is that the blend's composition has changed.
• BWrong: POE oil is bought and added separately; it doesn't come only mixed with virgin refrigerant.
• CWrong: no EPA rule bans topping off zeotropic blends after a 30% loss; recovering and recharging is good practice, not a 608 prohibition.
• DCorrect: a leaking zeotropic blend loses its components at different rates, so what remains no longer matches the original formula; recover it and recharge with fresh blend.

Zeotropic blends fractionate when leaking, losing components at different rates. Topping off a severely depleted system results in an incorrect refrigerant formulation and poor performance.

Answer: D. Refrigerant cross-contamination

• AWrong: a label doesn't change operating pressures; the risk is the next technician using the wrong refrigerant.
• BWrong: an outdated label can't cause an electrical failure.
• CWrong: a warranty isn't an EPA matter; the label issue is about identifying the refrigerant.
• DCorrect: if the label still names the old refrigerant, a later technician may add or recover the wrong one and contaminate the system or a recovery tank.

Labeling the system with the new refrigerant and oil is standard retrofit practice. Without it, the next technician reads the old data plate and may add or recover the wrong refrigerant, contaminating the system or a recovery cylinder.

Answer: A. The system will operate at significantly different pressures

• ACorrect: the substitute has its own pressure-temperature curve, so the system runs at noticeably different pressures unless controls and settings are adjusted.
• BWrong: an HFC can't turn back into an HCFC; that would require adding chlorine.
• CWrong: compressors don't adjust their displacement on their own to suit a new refrigerant.
• DWrong: a filter-drier doesn't rupture because the refrigerant changed; a vacuum doesn't burst a drier.

HFC blends operate at different pressure-temperature relationships than older HCFCs. A system retrofitted with a substitute will experience significantly different operating pressures requiring proper adjustment.

Answer: B. Expansion valve replacement

• AWrong: fan blade alignment has nothing to do with the refrigerant change.
• BCorrect: there are no true drop-ins; a new blend often needs a different expansion valve to meter it correctly at its own pressures.
• CWrong: straightening condenser fins is general maintenance, not a retrofit requirement.
• DWrong: thermostat wiring isn't affected by the refrigerant change.

Assuming replacements are exact drop-ins is dangerous. Differences in pressure, miscibility, and capacity often require hardware changes, such as replacing the expansion valve, to ensure proper operation.

Answer: C. Incompatibility between the original elastomers and the POE oil.

• AWrong: the stem says pressures are normal, so high discharge temperature doesn't explain seals failing everywhere at once.
• BWrong: galvanic corrosion is slow and attacks metal joints; it doesn't make elastomer seals leak.
• CCorrect: old elastomers that were conditioned in CFC and mineral oil can shrink or harden once they are exposed to HFC and POE, so seals are replaced during the retrofit.
• DWrong: with normal pressures, an overcharge wouldn't blow out many seals at once.

POE oil can cause older elastomer seals (used with CFCs) to shrink, harden, or dissolve, resulting in multiple leaks shortly after the retrofit.

Answer: A. A liquid and vapor mixture

• ACorrect: between the bubble point and the dew point, a zeotropic blend is partly liquid and partly vapor.
• BWrong: the blend becomes all vapor only above the dew point, and superheated only beyond that.
• CWrong: the blend is entirely liquid only at or below the bubble point.
• DWrong: subcooled liquid means a temperature below the bubble point, not between the bubble point and dew point.

For zeotropic blends, temperatures between the bubble point and dew point represent the two-phase glide region containing both liquid and vapor.

Answer: C. Residual mineral oil incompatibility

• AWrong: POE is the correct oil for HFC and HFO systems; having it in the system isn't what traps oil in the evaporator.
• BWrong: a fast evaporator fan wouldn't make oil pool or destroy the compressor.
• CCorrect: leftover mineral oil doesn't mix with HFC or HFO refrigerants, so it collects in the evaporator and the compressor runs short of oil.
• DWrong: an oversized accumulator doesn't cause oil to pool in the evaporator.

Leaving residual incompatible mineral oil in a system converted to an HFC or HFO blend leads to poor oil return and subsequent compressor failure.

Answer: B. Hydrogen, fluorine and carbon, with a carbon-carbon double bond

• AWrong: hydrogen, chlorine and carbon without fluorine isn't an HFO; HFOs carry fluorine and no chlorine.
• BCorrect: HFO means hydrofluoroolefin: hydrogen, fluorine and carbon, with at least one carbon-carbon double bond (the olefin part).
• CWrong: chlorine, fluorine and carbon with no hydrogen is the recipe for a CFC, the most ozone-depleting class.
• DWrong: fluorine and carbon alone, with no hydrogen, make a perfluorocarbon; the H in HFO stands for hydrogen.

HFO stands for hydrofluoroolefin. The molecule holds hydrogen, fluorine and carbon, and 'olefin' means it has at least one carbon-carbon double bond. That double bond lets HFOs break down quickly in the atmosphere, and with no chlorine their ozone depletion potential is zero.

Answer: D. A permanent shift in system dew point

• AWrong: fractionation changes the blend's composition; it doesn't stop oil from circulating.
• BWrong: subcooling doesn't keep climbing; the lasting change is to the blend's pressure-temperature behavior.
• CWrong: an expansion valve can't reverse.
• DCorrect: each vapor leak takes out more of the volatile components, so repeated topping off leaves a blend whose dew point and PT relationship have shifted.

Repeatedly topping off a high-glide blend after vapor leaks drastically alters the original refrigerant composition. This fractionation permanently shifts the system dew point and severely degrades cooling efficiency.

Answer: D. Failing to thoroughly flush the original mineral oil before adding the new polyolester oil.

• AWrong: a crankcase heater addresses refrigerant migration in general; leaving one out isn't the retrofit step that causes this.
• BWrong: an oversized filter-drier doesn't keep oil from returning to the compressor.
• CWrong: vapor charging can change a blend's composition, but it doesn't drain oil from the compressor.
• DCorrect: residual mineral oil doesn't mix with HFC, so it collects in the system and the compressor runs dry; the old oil should be flushed out during the retrofit.

HFCs are not miscible with mineral oil. Failing to thoroughly flush the original mineral oil before adding POE oil leads to poor oil return and eventual compressor failure.

Answer: A. Check oil and component compatibility and relabel the system

• ACorrect: there are no true drop-in replacements, so oil, components, and labels must all be addressed.
• BOil and elastomers may not be compatible with the substitute, so they must be checked too.
• CMixing refrigerants contaminates the charge; the R-22 must be recovered first.
• DCharging a zeotropic blend as vapor causes fractionation; blends are charged as liquid.

EPA test topics stress that there are no drop-in replacements for ozone-depleting refrigerants. A substitute can need a different lubricant, different components, and new labeling to show what the system contains.

Answer: C. Alkylbenzene or mineral oil for R-22; POE oil for R-134a

• ATopping off from one unit for another ignores which oil each compressor was built and filled with.
• BMineral and alkylbenzene oils do not mix well with HFCs like R-134a, so the R-134a side is wrong.
• CCorrect: HCFCs like R-22 use mineral or alkylbenzene oil, while HFCs like R-134a need ester (POE) oil.
• DOil must match the refrigerant; mineral oil does not circulate properly with R-134a.

EPA test topics pair ester (POE) oils with HFCs such as R-134a and alkylbenzene or mineral oils with HCFCs. Using the wrong lubricant leads to poor oil return and compressor damage.