See Figures 1 and 2
The air conditioning system has a high pressure (discharge) and a low pressure (suction) gauge port valve. These are Schrader valves which provide access to both the high and low pressure sides of the system for service hoses and a manifold gauge set so system pressures can be read. The high pressure gauge port valve is located between the compressor and the condenser, in the high pressure vapor (discharge) line. The low pressure gauge port valve is located between the suction accumulator/drier and the compressor, in the low pressure vapor (suction) line.
High side adapter set D81L-19703-A or tool YT-354, 355 or equivalent, is required to connect a manifold gauge set or charging station to the high pressure gauge port valve. Service tee fitting D87P-19703-A, which may be mounted on the clutch cycling pressure switch fitting, is available for use in the low pressure side, to be used in place of the low pressure gauge port valve.