CSLB C-20 HVAC ContractorCooling and RefrigerationMedium
A technician is adding oil to an R-410A residential compressor after a repair. Which type of oil must be used, and why?
- AAny oil viscosity-matched to the compressor, regardless of chemical type
- BPolyol ester (POE) oil, because R-410A is not miscible with mineral oil and requires a synthetic lubricant
- CMineral oil, because R-410A uses the same lubricant as R-22 systems
- DAlkylbenzene oil, because it is universally compatible with all refrigerants
Show answer & explanationAnswer & explanation
Correct answer: B. Polyol ester (POE) oil, because R-410A is not miscible with mineral oil and requires a synthetic lubricant
R-410A is an HFC blend that does not mix well with traditional mineral oils used in older R-22 systems. Manufacturers require POE (polyol ester) synthetic oil for proper lubricant return to the compressor and system reliability.
Why the other options are wrong
- A. Chemical compatibility, not just viscosity, determines correct oil selection.
- C. Mineral oil is used with R-22, not R-410A; it will not mix properly with HFC refrigerants.
- D. Alkylbenzene is sometimes used as a co-solvent with R-22 retrofit, not the standard for R-410A.
POE Oil for R-410A
Polyol ester (POE) oil is the required synthetic lubricant for R-410A systems due to its miscibility with HFC refrigerants.
- Mineral oil is incompatible with R-410A
- POE oil is hygroscopic and absorbs moisture quickly
- Keep POE oil containers sealed to prevent moisture contamination
Memory trick: R-410A needs POE, not the old MO.