If the AC light starts flashing and then the AC will not get cold on a 1991 Chevy pickup is the compressor froze up or is it just low on freon?

Actually I know of the indicator light which you speak Mine has just started to flash compressor not coming on I do believe that it is just low freon. will let you know more when I have mine tested.

There is not a a/c light on a 1991 chevy. Perhaps it's your alternator light? If the compressor is locked up it will more than likely burn your belt off.