I posted this on another thread but have lost track of it so will let it fly again.
I had the vacuum block behind the glove box replaced 12/2005. The original complaint was no hot air in the footwells and this fixed it. The last couple of months the air from the center vents was intermittent - seemed to depend on vacuum - and has lately ceased to blow at all. Plenty from the defrost and outer vents, however (and in Oklahoma with temps reaching 108, I'm more interested in cooling myself than my windshield). I accessed the vacuum block and all the individual actuators function well when direct vacuum is applied to them. Is it likely that the vac block has failed again so soon? Is my thinking rational, ie that since the actuators work with direct vacuum then the switching mechanism (vac block) is to blame? Will a vacuum leak on the supply line cause this? Thanks to all for helping me with other issues.
Chuck.

Yes, a vacuum leak on the supply line (green w/yellow stripe?) will cause this. There is a line (red w/grey stripe) which runs from the mess 'o vacuum lines near the brake booster to a vacuum reservoir. It runs across the firewall of the car - under the windshield wiper, behind the battery, and into the passenger side fenderwell where the reservoir is hidden. This line is noted for developing cracks, quite likely due to battery acid.

You need to start at the vacuum source and test the entire system to insure it is leak free. Any upstream leak reduces the amount of vacuum available to the climate system, with negative effects on its operation.

- JimY

Part of me is glad you said that and part of me isn't. The fix is more difficult but cheaper. That problem makes sense when you consider the gradual degradation of the system. I'll check it out. Thanks for the info, especially the specific vacuum line colors. It will make it much easier to troubleshoot.