My air-conditioner on 1996 Ford Explorer stopped blowing cool air. I've purchased an R-134 re-charging kit at Autozone with pressure meter. The pressure check actually showed normal reading (~35), still I managed to add some refrigerant, and the A/C was running good cool air for 2-3 days, but then again it's now just warm air. What could be the problem? Thanks in advance for your advise!

 

Well sounds like a sizeable leak there. First place I would check is the accumulator. If it has a rubber wrapping around it, peel back the rubber and see if it is heavily rusted. Ive seen a lot of them rust out and leak out the freon. If its rusted out then replace the accumulator and get the AC properly evacuated and recharged.
Other problem areas for leaks were, front compressor seal, manifold hose assembly, and evaporator.