This recommended practice provides technicians with safe and efficient techniques and general equipment recommendations for servicing Mobile Air Conditioning (MAC) systems in heavy duty and off-highway work machines. Presently, R-134a is the only approved refrigerant for use in mobile heavy duty and off-highway equipment and therefore this document primarily covers the servicing of R-134a systems. Since the technician may encounter other refrigerants a brief explanation on the identification safe handling of each refrigerant will be introduced.
The Heavy Duty, Off-Road Work Machine and Specialty Vehicle Mobile Air Conditioning (HD MAC) industry has typically utilized air conditioning standards, procedures and technologies developed by the automotive industry and SAE Interior Climate Control Standards Committee (ICCSC). These procedures do not always adequately address the unique challenges encountered by HD MAC technicians. Some of the challenges that should be addressed are: • Field service: The Off-highway and Specialty vehicle HVAC technician often services equipment in the field without a recovery, recycling & recharge machine. Instead the technician must use portable equipment but must still conform to EPA refrigerant recovery regulations. This is an area where a document specifying appropriate equipment and service techniques may be most beneficial to the industry and Heavy Duty MAC technician. • Internal volume: HD MAC systems typically have much greater internal volume and refrigerant charge compared to passenger car systems which may require different equipment and procedures to properly service. • Hoses/Moisture ingression: HD MAC systems primarily use flexible hoses. Fire trucks and other specialty equipment can have 120 feet of hose making moisture ingression (along with recovery and vacuum times) a significant concern even with Class I hose. • Air filtration/Cab pressurization and sealing: Off-highway work machines and Specialty vehicles often have a fixed recirculated/fresh air mix which is regulated by filter restriction and cab sealing. The ventilation system is a critical part of proper operator environment conditioning. It would be appropriate to include filter and cab sealing maintenance in HD MAC recommended procedures and training. • Leak Testing: Because of the larger internal volume on HD MAC systems, the procedure for vacuum and pressure decay leak detection may need to be longer than used with smaller systems.