The A/C control knob doesn't work anymore--the air only comes out of the defrost/dash area. How do I fix this?
Does temp and fan speed still work? The vents are vacuum controlled. Your truck has a vacuum motor on the passenger fenderwell. Make sure it is working and can build vacuum. If it can build vacuum find the leak. Most commonly it's related to the 4x4 hubs, which are also vacuum operated or something disconnected due to recent work.
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