Volvo Repair: Adding Coolant, 134a refrigerant, vacuum pump

Question
I have a 1996 850 GLT and want to add AC coolant.  Where is the pressure fitting located?  I understand there is only a low side fittng and not a high side.  

Thank you

Answer
     Hey Tim,
        Before you can add any 134a refrigerant you must vacate the system...or in other words use a vacuum pump to draw the system down....this is to allow a "FULL" charge.
  If you just add to the system...no real improvement will take place...you must test for leaks too.
        Unless you plan on continuing to keep your A C maintained...let a pro do it.

          Good luck.

               Bilbo