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I ran the vacuum with both guage set valves open for 30min. Now close both valves and remove the vac pump. Connect a R134a source to the yellow hose. You can use the 30lb can or the small 12oz cans. Bleed the hose at the manifold so there is no air in the line. open the low side valve slowly and let the R134a fill the system and bring the guage back to 0. Now close the low side valve and the valve on the R134a and reconnect the vac pump. Repeat the above once more for 15min then again for 15min and you're ready for the full charge. This time don't stop at 0. Let the R134a charge the system up to 60 to 80 lbs. You can put the can of R134a in warm water to help purge it.
Now you can start the truck and set the idle to 1500RPM. Set the cooling controls to max and high fan speed. Slowly open the low side valve on the guage set and let the refrigerant charge the system. You pretty much have to go by the readings on the guage set rather than the old R12 sticker for what a proper charge is. R134a operates at a higher pressure. I think mine calls for 3.5lbs of R12 but it would only hold about 2.5lbs before the high side pressure had reached 315lbs. That's too high, it should be kept under 300. There is a pressure relief valve on the high side of the compressor so therotically it should purge before any components fail but murphy's law always applies around my place. The low side stabalized at 35lbs.
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