problems with vents/ ac

hi guys,
i have a 99 astro and the vents and/or a/c doens't seem to be operating properly. The vents seem to be stuck on blowing the air to the window and the footwell. When you put the switch to forward or a/c it doesnt do anything. However whenever it is set to 'off' it does shut of the air so im not sure if it is te switch or some internal vent problem. The a/c could be a whole seperate problem, but im just hoping it might be something simple, or more precisely - cheap. Any thoughts anyone?
All help is greatly appreciated!!

When the HVAC control head loses vacuum, the system defaults to defrost. There is a 1/8" black plastic vacuum line that runs from the PCV valve, (in the left rocker arm cover), across the top of the engine, and connects to a vacuum tee under the hood by the A/C accumulator. The vacuum line dries out, cracks, and breaks. A section of rubber hose can be slid over the original hose at each end to repair the problem.

you are the man old master!

Thanks for your help again!

Well i finally got around to checking the A/C and it turns out that it wasn't the vacuum line that runs to the pcv valve (that one still has good suction) it was one of the other lines that go from the t joint.
The line that runs towards the dashboard is fine but the other which would have went to the HVAC control head (im guessing from the reply i got) has come off or been severed. Where exactly is the 'control head' of the HVAC system and where does the line join with it.
I don't have that much auto experience and use a hayes repair manual to guide me, so explain it like you were explaining to a slightly slow 10yr old, which is prob my mental age:rolleyes:.
Thank you again for all your help!!!!!

No problem ;) The vacuum source comes from the PCV connector. The vacuum line runs to the TEE fitting you found. The TEE may have a check valve built into it, or it may be close by, (inline). One side goes through the bulkhead, (firewall) and continues to the control head, (the mode switch in the dash that you turn to change air flow). If you remove the engine cover, you can see the lines and connections very easily. The other side of the TEE goes to a vacuum reservoir which is under the A/C accumulator, sometimes mounted to the frame, (black plastic ball shape). The check valve and reservoir make vacuum available to the mode switch under low engine vacuum conditions.

Hey old_master and others.
Well i got the vacuum line hooked up again and the vents and a/c started to work imediately. Thank you again. But ny joy was short lived because when i took my van for a short drive yesterday morning the #*$% really hit the fan!
The transmission started slipping and had trouble shifting up gears and when i put it in N or part the engine started struggling when it was idling and the oil pressure would drop with the revs.
I have had a slipping trans problem before (only about 3000miles ago) and took it to a shop who said they rebuilt the tranny and put in a new fly wheel. I think i was done, because that place has closed down now apparently.
I also just replace the ignition wires, sparks, distributor cap and rotor (Old_master you helped me with that a few posts back as well:rolleyes:) but i can't see how that would affect the transmission.:banghead:

Again any advice you guys can give me is really appreciated, i am very grateful to this forum.

If it ain't one thing... pull the trans dip stick and take a whiff, see if it looks or smells burnt. Should be clear red.

The trans fluid looks good, nice and clear red and doesnt smell burnt. Oh and the check engine light came on when it started playing up. I got a obd2 reader and the code is PO123 - TPS/pedal position sensor A circuit high input. Whatever the heck that means. Im pretty sure this is something im not gonna be able to handle myself but i would like to get as much info and possible causes so i will have a better chance of not getting ripped off this time.

Thanks again

Well i took it to a local mechanic and he said that it was something to do with the wiring at the TPS sensor, which he says tells the engine and transmission how much you are pushing down on the throttle.
So when the sensor is not reading when you put your foot on the gas, therefore the transmission didnt know when to shift up/down.
I took off the doghouse and fiddled with it and it seemed to right the problems! Took it for a drive and no problems. So i will replace the wiring and the sensor if it acts up again.
Thanks again for all the help