The purpose of this document is to establish guidelines for determining the critical R134a refrigerant charge for off-road, self-propelled work machines as defined in SAE J1116 and Agricultural Tractors as defined in ANSI/ASAE S390. It will develop a minimum to maximum refrigerant charge range in which the HVAC system can maintain proper operation. Operating conditions and characteristics of the equipment will influence the optimum charge. Since these conditions and characteristics vary greatly from one application to another, careful consideration should be taken to determine the optimum R134a refrigerant charge for the HVAC system.