My 98 Regency will only direct A/C (or heat) through the windshield ducts regardless of my trying to direct it to "bilevel" , "upper"or "lower" I have also recently had an intermitent check engine light that indicates "lean" condition. I suspect a vacuum leak and this might also be related to my duct problem. Any one out there have any idea'*?

205,000 one owner miles, many more left

Sounds vacuum related to me, some of our GM cars use vacuum to change to the other settings like bi-level, and when the vacuum modulator has a line break off then the air will default to the defroster.
I wish I could help more, but I am not an AC guy, I am sure one of our other members will post something helpful shortly.

William,

Thanks for the shout back, I have just now looked at my Aldata DIY and I see that my suspicions about the vacuum connection was correct It looks like getting access to this stuff is not something this old man needs to take on Thinking back I also recall that the passenger side air ducts have been acting up long before I encountered this latest malfunction so I think it'* time to visit my friendly GM specialist and open my wallet. I need to keep this car up as it has got to last forever Any repair is better than big car payments every month This car is comfortable, economical an actually looks pretty nice life is good

Very welcome, it is not too hard of a job to do, sometimes that modulator is repairable, but it may need replacing, a GM Dealer is going to take a chunk out of your wallet for it, not sure the actual price.
I am pretty sure the modulator is somewhere behind the glove box, getting to it is the hard part, will most likely require somebody to get upside down with feet in the air to get to it.
If you take it in have them inspect all vacuum lines, even any soft ones coming from the gas tank, on my 96' Park Ave I recently had to replace every soft EVAP hose, even the ones for my rear air struts compressor/air dryer, they were all deteriorated/dry-rotted.

there is no reason to pay dealer prices, there are a ton of good locally owned shops that will do just as good a job for half price.