Question about 1999 GMC Sierra

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Can some post the 1999 gmc sierra wiring diagram

The ac compressor will not turn on. the wiring is good from the compressor to the fuse panel under the hood. the relay switch and 10amp fuse are good. I did omhs check from the fuse panel relay plug in to the compressor plug and had O resistance for the green wire and .06 resistance for the brown wire. I swapped out the AC relay with the horn relay and no change, the horn worked with the swapped AC relay and the AC did not work with the swapped horn relay. when i turn on the switch in side the truck the AC light turns on and the fan blows air but the compressor does not. WHERE do I go from here?

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  • jfriceman Jul 03, 2009

    I did additional trouble shooting and there is no power to the A/C compressor plug in. I pulled the connector off the evaporator and jumped the connector and the A/C did not turn on; so I believe this eleminates the evaporator/low freon level. I'm thinking that there is a ground problem but don't kn where to look. Any suggestions?



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You don't have enough pressure in your system. odds are you have a leak someplace and the factory installed a saftey switch to keep the ac from running when there is no pressure. This way you don't end up burning up your compressor.

Posted on Jan 13, 2010


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