99 C23K Stuck inside/outside air vent flap.
 

The inside/outside air vent flap stuck in closed (recirc air) position. Can hear very faint slight movement when turning control knob from off position to on (any position). This model has the non-automatic climate control. Any suggestions? Does this mean dashboard removal?

Nope, I just found this while troubleshooting the manual climate control on my 2000 C230 K. Under the glove box, remove the black kickpanel like you are going to replace the cabin filter. Just aft of the cabin filter is a vaccum valve that controls the recirc flap. There is a green vac line that come from under the hood (via the vac resevoir forward of the passenger tire) and there is an electrical connector to the vac valve. When you press the recirc button, it energizes the valve, applies vaccum to the pod, that switches you to recirc. You can check the vaccum at the green line witht he car running. The vac source is the back of the intake on the driver's side, runs along the firewall, then to the vac resevoir, then back up and through firewall under glove box. Once you pull the black kick panel it's pretty easy to figure out. Chuck

99230k stuck inside/outside air vent flap
 

Thanks for the tip. I found the valve and it holds vacuum. I'm getting good engine vacuum. I can actuate the valve both ways by attaching attaching a rubber hose and sucking or blowing. My guess is that there must be a return spring holding the valve in a recirculating position until vacuum is applied and then it opens the flap. If this is right, then what?