R-134a SERVICE VALVES/PORTS
All vehicles with R-134a refrigerant use quick-disconnect service valves/ports. All R-134a systems use quick-disconnect fittings with sealing caps that thread into inside of service port instead of onto outside of service port.
The high side uses a large service port and the low side uses a small service port. See Figure. The R-134a service ports have internal metric threads to help prevent the accidental connection of R-12 servicing equipment.
There are 2 types of quick-disconnect service couplings which can be used on R-134a systems. One type of service coupling depresses service port valve when connection is made. The other type connects onto service port but will not depress service port valve until a knob is rotated. See Fig 1.