I have foul odor coming from vent when blower is on

SOURCE: air not coming out of vents

what your problem is that you have a issue with the vacume system, what i did was removed the bottom panel on the passenger side looked up and you will see a bunch of wires, look for a black box (should be right above your head by time you squeeze in there and it has a yellow/amberish type of color you will see that you can remove this its a rubber piece cut the pink tube on the side about 2 inches away from the plug assembly, and slide it into the blue tube this will bypass all controlls and shoot the air out of the front vents, you WILL NOT beable to set it to defrost max/normal or htr (mainly which vent flaps are where) this has worked formonths and the a/c acts as if its on normal mode to use the heat just slide the switch :) until you can test all the other equip this will keep you cool or warm

SOURCE: air conditioner blower

I found the vac lin broke under the battery

SOURCE: when A/C is on heat comes out of the driver side

I have a 99 Park Avenue and I had the same problem. The freon level was low.
Hope this helps.

SOURCE: 2001 buick lesabre-ac problems

• Assumed your AC unit is OK, but uneven temperature distribution. Try to throw the heater on an off severtime. A sticky valve on the heater would cause similar problem.
  
• Observe the RPM while parking your car. While the AC cut in cut out (or turn on an off). If it cause no load on the engine. The freon may be low or the compressor is bad. In this case only the intake side of the evaporator is cooler than the other side.
  

SOURCE: 2000 Buick Century . Blower motor works but no air

The louvers inside your vents are powered by a vacuum (?) that comes through a small rubber tube under your hood. I had to do some intensive googling to find this out. Usually what happens is that you change your battery, and accidentally pinch the rubber tube. If you're lucky, the mechanic will believe you before they start replacing parts. Maybe you can even find it yourself!