Miine does same thing but one of the repair manuals suggests that it may be the vacuum motor that controls/activates the various air direction doors. Or, a vacuum line leak in one of the controlling hoses. Or, the vacuum switch. I have lived with it not quite wanting to take the time to remove dash to get to suspect items to fix it since I run the fan higher than normal and it keeps temperature Ok except on very hotest, sunny days. May break down (eventaully) next vacation day(s) and have repair it. After I recheck the wiring and vacuum line schematics and access diagrams to same.
June, 26, 2006 AT 8:41 PM
A post from another site suggest that the 'most common cause of our Buicks' no air from mid vent problem is': " The most common fault is a vacuum leak in the small black plastic hose that comes from the engine compartment thru the firewall an in under the dash.
Look for the vacuum line going thru the firewall and back track it into the engine compartment and you will most likely find it broken or split somewhere in the engine compartment.
Find a connection and put a vacuum gage on it, You should have full manifold vacuum.&Quot; Which mechanic had suggested but I thought it too simple a fix. However, with hot weather here. I am going in search of that little black vacuum line with a leak in it and FIX it ---especially as it will not require opening up the dash!