You need to evacuate the system and draw a vacuum 1st. Make sure it can hold 30 in Hg. Once that is satisfied, you can charge with ES12A, about 20 oz total. This should yield low side pressures of 30-60 psi and hi side 200-250, depending on ambient temps.

You really need gages hooked up to low and hi sides, where you can charge with gages connected. All this after vacuum has been drawn on system.

134 and R12 have different oil, so you cant just drop R134 in a R12 system. This is why ppl use ES12A. Although for properly working system, the R12 is best as it will cool best.

Visit a good AC shop, they should be able to evac and charge with ES12A or Freeze12 for about $160, money well spent if you live in MIA!!

And from now on and until forever more : if someone is selling a car and they say "the AC just needs a charge", assume the worst. If it aint blowin snowballs, it aint working. Period. I cant tell you how many schmuks Ive had tell me it just needs a charge. It could be anything ($$) at that point, and you should always assume the worst. Personally, unless the guy seriously reduces the price by $1500, I dont touch cars blowing warm. The fix could be big $$ (and usually is, because if all it needed were a charge, the PO would of done that already).

__________________
Paul
Benz-less
I need an SDL !