Your air should be cold if there is any refrigerant in the system. The only time that it will get warm is if there is a leak and the coolant is leaking out. I did convert a friends car from R-12 to the 134 stuff and I was told that you need to pressurize the system before putting new stuff back in. We didn't and it never seemed like it was ever really cold like it should. If you do this yourself I would suggest getting a gauge so you know what the pressure is so you don't add more then the right pressure. Last thing I would put a bucket under there so in case something does come out you can dispose of it. IMO I would pay someone cause it's not that expensive, here in PA anyways($80). Good luck