A/C

1999 GMC SIERRA
4WD • AUTOMATIC
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BOB502
  • MEMBER
  • 22 POSTS
A/C is not working and warm air entering inside the truck cab when heater and blower are off. how do I check and resolve problem
Aug 22, 2011 at 9:56 PM
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JACOBANDNICKOLAS
  • CERTIFIED EXPERT
  • 110,175 POSTS
First, check to see if the AC compressor is cycling. If it doesn't, check the freon level. If it is too low, it won't work. If good, you need to check if the compressor is getting power. If it isn't check the cycle switch.

If it is working, check the blend door in the vehicle that is located near the heater core. If it is stuck, you won't get cool air, but rather, you'll get heat.
Sep 4, 2011 at 4:55 AM