Laboratory Wear Tests for Qualifying Automotive Air-Conditioning Lubricants for Use with Refrigerant HFC-134a

Three laboratory, block-on-ring wear tests were developed to evaluate potential lubricants for automotive air-conditioning (AC) compressors designed to use the alternative refrigerant HFC-134a. The tests were conducted in a pressurized refrigerant atmosphere using stepwise increasing loads. The three tests utilized steel rings and steel, brass, and aluminum blocks, respectively. Using multiple-variable, regression analyses, results from the three laboratory wear tests were used to explain wear phenomena occurring in a variable displacement AC compressor.

Correlations of the laboratory wear test data with data from compressor tests indicated that an optimized compressor lubricant should minimize aluminum and brass wear and maximize steel seizure loads. A variety of additives were evaluated using the three wear tests. Many additives were identified which could increase the seizure load and reduce steel wear. Several additives were capable of reducing brass wear relative to the base fluid in which they were blended. No additives were found to reduce the galling and wear of aluminum. Residual Clcontaining impurities in the HFC-134a refrigerant can increase the load at which seizure occurs in steel-on-steel wear tests.