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AC compressor comes on when turned off


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csterl01's Avatar
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November 27th, 2010, 6:29 PM   #1  
AC compressor comes on when turned off

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.

 
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November 27th, 2010, 10:20 PM   #2  
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.

 
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November 28th, 2010, 8:17 PM   #3  
Note sure if the 99's do it but my 07 will turn the AC on if the defrost is selected ...

 
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November 29th, 2010, 7:43 PM   #4  
They've been doing that for a long time to keep the seals lubed. I think it quits around 35*.

 
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November 29th, 2010, 9:15 PM   #5  
I just thought it was to help dry out the air going to the windshield...

 
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November 29th, 2010, 10:42 PM   #6  
That too. Especially when it's cold out and you have a load of people.

 
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November 30th, 2010, 7:01 AM   #7  
Posted By: 73shark 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.
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?

 
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