$40 for a can of Freon? I think /not/.

1990 Dodge pickup. Drained out the R12 slowly as not to lose any oil, changed the fittings and refilled it with Envrioseal and it blows at 38º. Thats plenty cold for me.
Once the air temp reaches 32º, the evaporator will freeze up, and it won't cool anymore until the ice melts. I didn't change anything else in the system, and didn't pull a vacuum either. It's been 10 years now.

I have 4 fresh cans of DuPont R12 freon sitting in my garage, but can't find anyone with a gauge set or a can tap to put it in for me locally.
Someday I'll switch it back to R12.

George