Re-filling A/c Unit With Refrigerant

[diesel2k]

Hey guys,

I noticed my AC was blowing out hot air so I tried filling it back up with AC refigerant. I bought the refigerant at an Auto Zone. It came with a trigger, hose and a gauge to measure the AC fluid level. I connected the hose to the LOW Pressure Vavle and noticed that the freon was going in then all of a sudden, the gauge dropped back down to it's original level of indicating low AC levels. My dad said it was possible that the AC pipes on the truck are filled up with air and needs to be vaccuumed. I also noticed there was a third valve on the compressoer. Does anyone know what this valve is. I know it's not the high pressure. Any suggestions on what I can do fix the problem? Thanks

[mburnickas]

Did you vac the line to start with?

[diesel2k]

No, How do you vaccuum the line? Is it easy to do myself?