Automotive Air Conditioning Information Forum

Hello,
My 2004 Silverado SS developed a leak in high pressure fill port and I ignored it for so long that all Freon leaked out. Prior to this, HVAC system work flawlessly. I took it to reliable AC shop yesterday and had port replaced, system vacuumed and refilled. Pressures were correct...but guy noticed immediately that the system would cycle on properly when the AC was first turned on, but once it cycled off...the compressor would not cycle back on! He double checked pressures and they were correct with compressor on, as well as off. He tested and replaced relay, sensors and checked fuse. Then he hooked up diagnostic tool to search for codes...No codes. When relay is removed and hot wired...compressor kicks in immediately. His only thought was the HVAC control unit...any ideas before I go buy one and try it???
I appreciate your time to read and what help you can offer!
Jimmy

My first thought is to check the clutch gap. It may be too wide. The first time it comes on, everything is fine. After that, the coil is hot causing more resistance and a weaker magnetic pull on the clutch. After it is off for a bit, it cools off enough to work again. The relay also causes some resistance, so when it is bypassed, it works every time. An easy way to check this theory is to see if there is power to the clutch when it is not spinning. If the computer thinks it is spinning, there would be no code. I don't get into the electronics enough to even know for sure that there would be a code on that truck. Good luck!

No codes get set for relay problems or air gap too wide issues on the C/K platform. Very, very common for wide air gap- I've done maybe 4 or 5 a season for that era truck. Remove a shim and get another 100k miles out of compressor.

Thank you both! I checked the gap and it appears fine. Even tried the bump with a stick trick...to no avail. But, what I did find and it appears to have corrected issue, was a programing issue with EFIlive. Prior to my high pressure fill valve going bad, I had added electric fans and downloaded a '06 SSS stock tune for the electric fan programming. Not knowing what the settings should be, I assumed they were correct. But, when I compared the numbers to my '02 Z06 there was a glaring error. The fan on with AC was set at 284 on SSS settings, but 185 on Z06! Bing go...compressor would try to kick on when demanded, but because computer was not seeing fan on...it was immediately shut out. I may have terminology wrong...but I think the reasoning is correct. At least it appears to be working correctly...now.