My 1999 Silverado Ext cab 5.3ltr a/c runs very cold then goes warm, turn off compressor for 15-30 sec and it will go back to cold, I tried adding Freon with no change. Any suggestions appreciated.

 

Do you have a leak near the firewall. my old truck would leak freon as soon as I put it in.

 

It seems to be holding the Freon.

 

Its possible the compressor is going out... I just recently replaced the compressor in our minivan for a similar situation, it would get warm at a stop but sorta cool when driving...
Do keep in mind that unless you know you have a leak, adding Freon will over charge the system and kill the compressor, better to have a low charge than an over charge....

 

thanks for the help

 

Get a set of gauges on it, they should read fairly steady, if you get a lot of needle shake and crazy readings its very likely the compressor or blockage....
FYI Rock Auto has pretty decent prices for AC "kits" that contain the compressor, dryer, expansion valve and o-rings for pretty affordable prices if it turns out that you need to go that route...
Keep us posted on what you find...

 

thanks in2pro for the advice

 

I had the same problem with my 2000. My problem was the clutch would slip when having to work hard. Instead of just replacing the clutch or adjusting the "air gap" I read about I decided to go ahead and replace the compressor, accumulator/dryer and the orifice tube since it had 196k miles on it I figured it was time for a replacement.