Defrost knob not going down
 

My center defrost knob ('79 Euro SC) is stuck in the up position. Has anyone dealt with this before? With the defrost off the knob does not go down. Don't want to force it, but this is the wrong time of year to have the heat on all the time.
Thanks for any insight.

My 77 911s did this after sitting for a few years.... don't use heat during the unused winter months. I went inside the front hood and lubed the cables with a graphite liquid used for motorcycle cables ........ the can has a long needle spout so you can apply the liquid to the inner cable and let it run downhill along the cable. I believe the product is called bike-aid, and is available at most MC dealerships. Hope this helps.... have used it for all kinds of cables, including e-brake cables , heater cables etc.

Are you refering to the dashboard slider or the lever between the seats?
If the lever between the seats is in the up position and the dial on the auto heat is in the off
position then the rod has come off the servo motor.
There is an access cover on the passenger side (better to get at with the seat removed) once your in you will most likely see the rod has popped off.

Thanks, guys. I knew "knob" didn't sound right when I wrote it.
In fact it is the LEVER between the seats. I'll pull the passenger side seat and have a look.

Be surprised if it was anything inside the cabin. I make a point of moving those levers (two separate ones in a '77) through their full range of motion every time I drive the car, just to keep them moving. Full heat to start, knock off gradually as I drive, off to park, rinse, repeat :)

The driver's side recently just got stiffer and stiffer over a day or three, until it wouldn't pull up with reasonable force beyond where the tension started to be felt in the piano wire.

Closed both flappers up, short squirt of white lithium grease on the center of the flapper box, even shorter squirt on the cable end, open them all the way (they moved freely instantly), another squirt to cover the inner faces of the flapper discs (so less prone to bind) and done.

They both move with almost no resistance now. Slight "hot lithium grease" odor with the heat, but I think that will pass quickly...