Get an A/C thermometer (or equivalent) about $4. Start truck, turn a/c on max, run truck at 1500 rpm, test output air. Now take a powerful house fan (or such) put it on boxes (or such) so that the fan blows on highest speed directly into condenser. Test output, if significant change in temp try putting a big a$$ electric fan or a double electric with one side only on during A/C mode (saves gas). If no, or very little change then you may have a significant amount of contamination or non-condensables. Refrigerant must be installed by weight. R-134 is 80% of r-12 charge. We'll say it takes 3.5 pounds, then 3.5x.80=2.8 pounds of 134a.. If you have the gauge set and a vacuum pump, or know someone that does. Change the oriface tube, and vacuum the system down to 29 inches of vacuum and let it run for an hour to get all the contamination and moisture out of the system. IF YOU DO NOT GET OIL OUT OF THE SYSTEM WHEN YOU VACUUM THE DO NOT ADD OIL. If some oil comes out the only add the same amount back in. Let the system sit with vacuum for about 5 min or so and check vacuum on the gauge. Don't forget to turn off the center valve on the manifold set. It should not have any drop in vacuum. If it does you have a leak. Recharge system with prescribed amount of refrigerant and test again.. Should be quite cool.
Sorry about the long post but a lot, if not most of the time people that do the conversion they just dump and go, and that won't work right.
