86 420 SEL AC Problem
 

First found AC won't turn on until accelerated to high speed, then even high speed wouldn't work, until about 15-20 minutes,, sometimes after reduce speed, and suddenly with a hssh sound it's on. After turning on, seemed the higher the car runs, the cooler the air is. Went to mechanic, said Freon was only 1 lb, suggesting me change to R134a, agreed, but after that same problem. I felt the belt a bit loose, but the mechanic said it's ok. but problrm still there. I told mechanic there are engine speed switch and shut off switch in the ac, he seemed didn't know. He added less R134a, is that a poosible reson? But problem exact as before, also after ac on, if reduce the speed, it can turn off again and still hard to start up. Any help would be appreciated.