I have a 1999 Silverado LS I am the original owner. . Recently the AC would stop blowing real cold air, after first turning it on, but would blow cool-ish air. If I shut off the AC for a few mins., and then turn it back on, it would blow cold but eventually back to only cool. I did this on the recent trip for 2 hours of freeway driving. I took it to tire and repair shop and they recharged it. It seemed to work ok for one day and now it was back to the same old thing. I don't recall ever recharging it since I owned it brand new. It seems to be worse at freeway speeds. There is more but let me start from here. Any help?