AC in my 91 B2600 not working. AC button lights up on the first press and compressor comes on as the engine idles up slightly. Then after a few seconds engine idles back down to normal and doesn’t idle up again. Guy I bought it from says they converted it to R134, and it never really got cold after they added R134. I think it’s the compressor since it’s not clicking on and off after that initial one time. Truck only has 90000 miles and completely untouched. And wasn’t driven much at all. Any help is appreciated.