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Check for vacuum leak either under hood or under dash Check for bad vacuum actuator under dash Check for bad selector switch in dash
Sounds like you may have a bad selector switch or you may want to check the vaccum hoses in the engine compartment.
Perhaps a bad selector switch If it is a bad selector can I replace the one on the dash (the one for selecting the vent) or is there some control module elsewhere in the vehicle that I can replace to fix the problem?
Under the passenger side dash, just behind the glove box....
Check for a vacuum leak either under hood or under dash Check for a bad vacuum actuated motor under dash Check selector switch
Check for vacuum leak either under hood or under dash Check for bad vacuum motor underdash Check for bad selector switch
Bad blower motor? Plugged air duct? Bad selector switch? (air being re-directed) Bad vacuum acutated motor under dash? Vacuum leak under hood or under dash?
Check for a vacuum leak either under hood or under dash Check the operation of the vacuum controlled motors under dash Check the operation of the selector switch Defrost is the default position for this system
Check your headlight switch. Sometimes the switch goes bad and the dash lights won't light. Replace the switch for the fix.
If the truck is manual. There are a couple of place to check. A bad ignition switch, bad clutch interlock switch or a bad starter relay. If it is an automatic. The selector switch could be bad.
Bad switch?
You can tell if your fuel pump shutoff switch is bad, if the fuel pump does not shut off when you flip the switch. You can also tell if the switch is bad by looking at the wire connections.