The Lubricant Equation for New Refrigerants

December 7, 2009
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The phaseout of ozone depleting refrigerants has impacted air conditioning and refrigeration equipment design in many ways. One of the most significant changes to these systems is the transition of the compressor lubricants. Use of an appropriate lubricant is important when servicing, installing, or retrofitting a system.

What follows is information that may be helpful as general background information on refrigerant lubricants. However, always follow OEM recommendations for proper lubricant selection.

Mineral Oil: Mineral oil has been the lubricant of choice for systems utilizing many of the CFC and HCFC refrigerants. Both CFCs and HCFCs tend to have adequate miscibility with mineral oil, helping to ensure acceptable oil return under normal operating conditions. Sometimes a synthetic lubricant (i.e., AB or POE) is required under certain conditions such as reduced miscibility with CFC retrofit blends or high discharge temperatures with products like HCFC-22.

Alkyl Benzene: Alkyl benzene is a synthetic refrigerant compressor lubricant for use in some very low temperature systems where mineral oil would not work well. Typically, alkyl benzene has better miscibility with HCFCs than with mineral oil, resulting in more reliable oil return. A partial oil change from mineral oil to alkyl benzene may be beneficial to improve oil circulation.

Polyolester: HFC refrigerants serve as replacements for the ozone-depleting CFCs and HCFCs. However, both mineral oil and alkyl benzene have poor miscibility with HFCs, making oil return with these products unreliable in many systems. POEs are synthetic oils commonly used in new HFC systems and for retrofitting CFC and HCFC equipment to HFC refrigerants. Special care must be taken when using POE oils due to their quick absorption of moisture when left exposed to the atmosphere (hygroscopic).

Polyalkylene Glycol: In addition to POE oils, polyalkylene glycol (PAG) lubricants are used with R-134a in automotive air-conditioning applications. Like POEs, PAGs are hygroscopic synthetic oils and must be treated with care to minimize exposure to moisture. While both POEs and PAGs are used with R-134a in automotive systems, the two oil types are not interchangeable, and should not be mixed. Also, PAGs cannot and should not be used in stationary systems because material incompatibilities may result in system failure. PAG can only be used in auto air conditioning.

MATERIAL COMPATIBILITY

Whenever retrofitting an air conditioning or refrigeration system, compatibility of system materials is always a concern. Items such as elastomers, hoses, and filter-driers respond differently to different refrigerants and oils. For these reasons, before performing any refrigerant retrofit, contact the OEM for specific recommendations.

LEAK DETECTION

Leak checking should be a routine practice whenever performing maintenance on or servicing an air conditioning or refrigeration system. As elastomers and other sealing components may react differently to new refrigerants and oils, leak checking should always be performed after any refrigerant retrofit.

Certain older style leak detectors have difficulty detecting newer refrigerants. It is important to verify whether or not your leak detector is rated for the type of refrigerant (CFC, HCFC, or HFC) you will be working with. Also, some refrigerant dyes are only compatible with specific refrigerant oils. Always check with the manufacturer before using a leak dye in an air conditioning or refrigeration system.

[Editor’s note: This information was supplied by Arkema, www.arkema-inc.com.]

Publication date: 12/07/2009

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