Well, my '95 ranger used to have the coldest A/C of any vehicle I've ever driven, it's r132 not r12. A few months ago, it inexplicably stopped working. I checked the pressure, and it was perfectly fine. I suspected the High or low side pressure switches were bad, so I jumped them, and still couldn't get the compressor to kick on at all. I then wired 12v directly to the compressor, and that did the trick! Instantly started shooting snowballs out of my vents. Plugged everything back together, and it was back to not working. I left it like this trying to find a reasonable a/c mechanic, and stopped fussing about it and just dealt with the heat. Until just the other day....

Now, when I first start my truck, the A/C will blow cold and hard, and will remain that way until I start moving. I can drive up through the gears to third, and by then it's tepid. I can then stop, shut the engine off and restart it and it will be back to blowing cold again. I am at a loss here....

 

compressor clutch may be worn out. are you the only owner? the pag oil in the system normally keeps the compressor from wearing out so fast, a lack of it may cause excessive wear. if the compressor is working like it should right now, and you still get tepid air, may be evaporator freeze up. those are a couple of possibilities.