Dodge Repair: low intale vacuum, vacuum ports, vacuum lines

Question
I am working on a 97 Dodge 2500 with a 3.9 engine. The a/c goes to the defrost under a load and I have checked the vacuum lines going to the ported switch in the a/c control panel. All the lines are good (with no leaks) but the intake vacuum is just too low. It has a aluminum plenum with only 2 vacuum ports. One port feeds the PCV and the other port feeds everything else. I blocked off the PCV port and I only have about 8 inches of vacuum at an idle. When I brake torque the engine to about 2000 rpms, my vacuum drops to almost zero.I thought that the convertor could have been blocked so I did a backpressure test at the upstream o/2 sensor and I am reading no backpressure here at an idle and also at 2000 rpms. This engine just doesn't have enough vacuum to work the actuators on the various a/c doors. There is a check valve in the port feeding the a/c system and the vacuum canister does not lose vacuum when tested. This engine just does not have enough vacuum, PERIOD. Any ideas where to look?

Answer
it has plenty  U have a bad check valve  fallow the vac lines to teh fire wall where they go into for the AC head. then fallow it out to the source and in that line u will find a check valve  it has an internal leak and will not have the vac pressure required for the ac head to work. Plus  i bet u don't have cruise control as well huh? IF u respond to this  I will get the part number from work and relay it to u because its a big pain in the ass to find it on the computer system unless u get some one that just knows the number right off hand.