I love my 99 Tahoe, it has been one of the most dependable vehicles I have ever owned. For the past few years, if you turn the fan switch off and leave the AC button pressed, the compressor will cycle on and off at will. This is manual air with rear air. The AC indicator lights goes off and on with the compressor. Depressing the AC button cuts the compressor off completely.

Any ideas? I'm real picky about my ride and want everything to work as it should.

 

Welcome to the forum.

Not familiar w/ 99s but not sure that when you turn the fan all the way down, it goes off. I think it probably just goes to the lowest speed in which case the compressor will cycle to keep the evaporator from freezing up. If you can turn the HVAC system off, the compressor shouldn't run then. But this all based on some logical assumptions. Others may be more familiar w/ your system.

 

Note sure if the 99's do it but my 07 will turn the AC on if the defrost is selected ...

 

They've been doing that for a long time to keep the seals lubed. I think it quits around 35*.

 

I just thought it was to help dry out the air going to the windshield...

 

That too. Especially when it's cold out and you have a load of people.

 

On the 99's it is supposed to shut off vs lowest speed. There is no other way to shut the entire system down as on later systems, where the function control has an off position. This is when the fan is turned to off and nothing other than fresh air should be working. Does anyone know where I can get a wiring schematic for the AC controls?

 

The defrost runs the AC compressor intermittently to remove the moisture actually causing the frosty windows. Sure, regular air can work, the use of the AC comp is much mo quick-er-er.

Physics, yo.
Or something like that.

My deal is poking stuff with das blinken lightzen while steeling my will for the evenual 12v jolt.
Sure, physics sorta governs how electrons and protons do their thing also, but lets not get off in the weeds.