I have a 1994 F 150 with the 302,the air cond. works some times for a little while. Last year it worked good. Ok I added a can of stop leak and thats when the problems started.Low side presure is 40 lbs, once when I checked it hot, it was over 100 lbs. I need some things to check and do.

 

Checking the pressure hot is only good to see if you have air in the system. When you check it hot or not running you should try to do this first thing in the morning when the truck as sat over night so that everything is the same temp as ambient temp. Cross that pressure on a PTR chart to the corresponding temp for that pressure. It should be with in a couple of degrees with in ambient temp. More than a couple of degrees and you have air in the system, the wider the spread the more air.

It is really helpful to know the discharge pressure as well as the suction pressure. A suction pressure of 40 is not abnormal in warm weather, but with out the high side it does not tell the whole story.

Hit your condenser with some degreaser and hose it off to make sure it is clean. Check your fan clutch, make sure it is functioning properly.

And if you can get the high side pressure with it running I can tell if it is properly running

Matt