Is your truck a 4X4? If so does it have the ESOF (Electronic Shift On the Fly) transfer case (knob on the dash, not lever on the floor)? The A/C Blend doors are actuated by vacuum and so are the hubs. If you have a vacuum leak, (quite often at the wheel/hub) the blend door does not work. If you have manual hubs, you may still have a vacuum leak, or the vacuum pump is not working. The vacuum pump is a small box and motor on the passenger fender between the battery and the AC box on the firewall. If you have the hood up and turn on the key to run, with the engine off, you will hear the pump run to build a vacuum, it should turn off after 30 - 60 seconds, or mine does at least. If it runs constantly, you have a leak. This can also burn the vacuum pump up also.....To help us all out goto the blue line at the top of the pages and click on User CP and fill out your signature with your trucks information like mine
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