Intermittent failure of A/C and Heater control

[jbeenemd]

I have a 2004 Sierra 1500 extended cab 4X4 with the 5.3 Liter V-8. When I got it in 2007 it had around 39,000 miles. I just turned over 140,000 miles. In the 9 years that I have had it I have found that on the heater side of things I sometimes have to turn it up to 90 degrees to get the heat started and then dial it back down however if I turn it too low then it only gives cold air and have to start the process again. Marked it up to a bad rheostat. The A/C works great at anything over 30 MPH. When in the city doing stop and go it is almost better to open the windows. Thought that it just needed some freon. Had recently moved and all of my tools were in storage. Took it too a local established auto A/C repair shop. The tech came out after looking at my truck and asked me if I had put freon in it myself. Well, no I had not. Was initially told that the pressure were extremely high on the "high-side". Told me that it was over filled, He then bleed off until the pressures were down to normal. Can't remember but for some reason I think that I was told that the low side was too low. Did not help with the A/C. His boss/manager then told me that the compressor was bad and wanted to sell me a new compressor to the tune of $1000. That was in the summer of 2007. Did not have the time to leave it there at the time. Since then the A/C has continued to work when the truck is moving. Just not well when sitting still/hence the poor performance in the above shop. I don't think they knew what to do. Have been told that there is some sort of filter in the system that may be plugged. Not taking about an air filter but a filter or maybe a valve some where between the high pressure side and low pressure side. Is this true? If so where is it and what is involved in replacement? Another problem that happens once or twice a summer is that the A/C will not cool at all. Blows air seemingly hotter than my heater could produce but then it is already hot for me to turn on the A/C. This afternoon when getting off work wanted to run the A/C just because of the humidity. HOT HOT HOT air from the A/C. Tried several times on the 45 minute trip home to turn on and then back off. No luck in getting cool air. After getting home, changed cloths and off to the grocery store with my wife. Tried the A/C and now the damn thing works!?!? Switch problem? Has only happened maybe twice a summer. If was more often or permanent issue then would be easier to trace. Suggestions welcome.

[muddkatt]

My 2001 would work sometimes, then stop. It finally quit all together. It was the compressor clutch that was failing. The only filter that could be changed is the orifice tube. If its stopped up, you got bigger problems than a clogged filter.