Sticky door. Quite a few members have fun into this and fixed it.

It could also be a vacuum problem. Without adequate consistent vacuum to the climate controls, the system can default to the defrost vents. I would check to see that the vacuum system isn't compromised from the throttle body to the firewall to the climate control.

Is it just the way I review these messages - that the photos submitted take up the entire content of the page and one cannot read the comments.

I would post an answer here BUT, because of all this "Double Posting" my answer doesn't make any sense & is impossible to read!

Let'* try this this way instead.....Based upon what I've read here. It sounds like the HVAC Control Head itself is at fault. If so, then some trouble codes should be registered in the PCM to back this up.
First Read This:
http://www.bonnevilleclub.com/techinfo/?article=45
Next Read This:
http://www.friedpoodle.com/ba/forum/viewtopic.php?t=165
Then Read This:
http://www.friedpoodle.com/ba/forum/viewtopic.php?t=164

actually,

my prob. has returned. i have the fan speed setting set to HIGH (not auto). i turn left...fan blows full blast....i hit a bump...fan blows full blast...driving normally...fan blows weakly or not at all..but occassionally blows at the setting it is supposed to. someone mentioned earlier that the fan might have a dead spot. would replacing the fan/motor fix the issue? this has nothing to do with vacuum since my doors properly switch the air flow to the floor, vent, or windshield. that all works fine....the fan is the problem. and it'* pretty cold in michigan!

A fan with a dead spot? Not possible. If a winding went out, it'* a goner.

so what is it then????? arg. :?

Sorry, but I have to disagree here; a dead spot doesn't necessarily mean a broken winding. Our '96 Trans Sport blower motor would simply not run until I popped the hood and tapped it with a stick, at which point it would start spinning just fine, until the next time we shut down the van. Finally got around to pulling the thing out (on a '96 Trans Sport that is _not_ fun), and blasted it thoroughly clean with carb cleaner by squirting the brushes and armature through the cooling holes. I also added a drop of oil to the bearings, and it ran fine for about 18 months after that. When the symptoms returned (wouldn't start by itself until I either tapped it with a stick or drove over some bumpy road), it had another cleaning and it'* back to normal again.

So basically the "dead spot" may be just dirt. It'* easy to pull the blower on a Bonneville so I would just yank it and blast some cleaner in there.

BTW, your problem _is_ the blower motor, if turning corners will affect its operation, because the centrifugal force of cornering is shifting the squirrel-cage fan on its shaft. I think your blower is probably worn out (shaft tolerances are probably shot), but with a cleaning and a little oil you may get it working again and save yourself some bucks.

That'* not a bad idea. Give it a whirl. But if it works, I'd buy a new motor right away. No point in waiting for the inevitable.