Chances are its the port on the manifold on the back side of the compressor....unless there is 2 ports there... however, if you follow the line coming from the firewall to the compressor then thats the low side....the line going from the compressor to the condensor(the smaller radiator infront of the radiator) that would be the High pressure side..... normally you do not need to check the high side if things are working properly, the low side is used for charging the system with refrigerant. Pressure reading should be in the 30-35 psi range....and should not drop below 26 psi(or so) when the engine rpm's on the higher side(4000-ish rpm), if the low pressure switch works, it will turn off the clutch to the compressor untill the pressure returns to something higher.
NOW realize, i am not an A/C EXPERT, i've tinkered with my vehicles and a few buddies....so your milage may vary, and please, if anyone has something to add/offer, feel free.... youtube does have some videos that might help.
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StingrayJim
NCM Lifetime Member #1936
Stingray's '76���������������������������� StingrayJr's '78���������������������������Lil Red '94
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