On every car A/C system I have worked on, the HIGH pressure side or DISCHARGE has the smaller diameter hose or hard line. The LOW side is the larger diameter. Just that question is why on later cars they used two different sized fittings to hook up the gauges. You want about 30-35psi on the low side with the engine at high idle (about 1200 to 1500rpm). Don't over charge... and don't put in too much oil as it can cut efficiency.

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My Truck.. 2007 DODGE, 5.9 Cummins, 6spd stick, 4X4. My car..1977 240D, OTHER WHEELS...1955 VW Oval window bug, European Delivery (Holland) with a 1700cc, 2 barrel, Porsche drum brakes. 1939 WILLYS Pick-up. 1967 Triumph 200cc Tiger Cub. 1976 Honda 550F 4cyl Motor Cycle.