My A/C used to work when I put 134A into it but it got to where it would not hold a charge for very long. I took it to a mechanic and he said it was the evaporator and it would be 500 dollars to fix it. I got it home and it worked around town but when I got on the interstate running high RPM's the A/C didn't work at all. So I took it back to him and he put another 1/2 can of refrigerant and said he must have undercharged it. I took it home and drove it for a couple of days then the system would work sometimes and not others. I took it back to him and he said it was low on refrigerant and he thought it was leaking at the high pressure switch so he replaced it and charged me 90. 00 dollars. When I first got it back the A/C would work sometimes and not at all others times but now it works about everytime I turn the truck on but the lowest the truck temperature gets down to is 58 degrees on a 85 degree day. Is this acceptable and if not what do you all think, please help thanks?