I have a 1991 Pathfinder 4x4 in near perfect condition and I can not get any R12 into the low side,I know it`s low because of the amount of cool it puts out also the compressor keeps cycling while idling. I have a full can of Freon and it comes out of the end of the hose when I open the valve while not hooked up. .I pushed the center of the Schrader valve on the van and it will burp so I know it`s not stuck. any thoughts?