Most vehicles, including yours, has a 'mode door' that has a vaccum actuator to make it move. Either the vacuum is not getting from the engine through the ac controls to the actuator, or the actuator itself is bad and is leaking vacuum.
Poke around under the dash and listen for any hissing sounds...maybe you get lucky and the vacuum hose just fell off or split at the end.
Earl
February 2008
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