The Falex (pin and vee block) machine is widely used by equipment manufacturers and oil suppliers in efforts to simulate lubrication in refrigerant compressors and to screen refrigerant oils. Little of this information is published-probably because the validity of the tests is not established and also because the effects of the test parameters are not well understood. This paper discusses these effects with reference to the fundamentals of boundary lubrication. Behavior of typical additive-free refrigerant oils is described, and laboratory simulation of heat pump lubrication under high oil dilution using a modified Falex tester is presented.