Does the cabin air recirculation button on the Climate Control Unit seem to not do anything, a known problem with a quick fix.

The button on the Climate Control Unit (CCU) with the little circular icon is designed to turn on cabin air recirculation. 

It controls a solenoid air valve behind the dash that then controls a vacuum actuator behind the CCU in the dash. The actuator's pull rod is attached to the vent mechanism by a black plastic push rivet. The actuator's arm comes loose from the rivet and the mechanism is no longer actuated, see the below picture. This is a very common failure and when it detaches the air recirculation button on the Climate Control Unit no longer functions. 

Photo credit user "Alpha 40" on Rennlist

The fix is to remove the black plastic push rivet if it hasn't already gone missing and loop a tie-wrap through the hole the rivet was in and then through the metal arm's hole and close the tie-wrap. This is the repair I did and it has lasted for years. Some go to the extra effort if using a machine screw and two nuts as jamb-nuts to work as a pin in the same way.

It is so common a problem I suggest everyone test their recirculating air button. To test it run the car a little to build vacuum reserve, park, and turn the engine and cabin blower off but leave the ignition on. Press the recirculation button on the CCU and release it. One should hear a "thwack" sound as the actuator moves the air control valve. No "thwack" and the arm has come loose.

The first section on this page discusses how to remove the Climate Control Unit (CCU) to gain access to the recirculation acuator for servicing.

Earlier cars didn't have the actuator mechanism and therefore no "thwack" so if you have an early production 1995 or an earlier model year car the mechanism may not be present or present but not attached. If you care to check just pull the CCU and look behind it while pressing the CCU's recirculation button.

•  If you see the actuator's arm move and not open the vent it has become detached; 
• If your car is an early production 1995 model or earlier and the actuator's arm doesn't move and the actuator or some of the arms are detached or simply not present the mechanism may just be something that was orphaned at the factory during a design transition/part supersession and no repair is required.

Here is a little video supplied from Rennlist by user "bobpyb" that shows the actuator mechanism in action:  https://youtu.be/-jusuIO3wuY

Also if any of the pushbuttons are broken on your CCU they can be replaced Here:
Replacement CCU Push Button Switches

Andy

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