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J3078/4 specifies a uniform test method for measuring the contribution to operator environmental temperature provided by a heating, ventilating and air conditioning system operating in a specific ambient environment. The method might not determine the complete climatic environment of the operator since this is also affected by heat load from sources other than those on the machine, for example solar heating. J3708/6 is to be used in conjunction with J3078/4 to determine more accurately the complete heat loading on the operator enclosure. Minimum performance levels for the machine’s operator enclosure heating, ventilating and air conditioning systems are established in J3708/4.

This recommended practice provides technicians with safe and efficient techniques and general equipment recommendations for servicing Mobile Air Conditioning (MAC) systems into Off-Road Self-Propelled Work Machines as defined in SAE J1116 and Tractors and Machinery for Agriculture and Forestry as defined in ANSI/ASAE S390. Both refrigerants R 134a and R-1234yf are covered. Many service procedures are similar for both refrigerants but recovery, recycling, charging, electronic leak detection and other tools can be unique to each refrigerant.

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.