Just some general thoughts on this.
If the cable binds on too tight a turn, you will probably break off the retainer at the dash control. New dash control needed to repair.
If the system is still intact, but stiff, spray lots of silicone on the cable ends and work the cable back and forth.
It will be the pushing motion that binds the cable.
I added a spring to the heat box linkage to help pull that open. The cable has no trouble pulling it closed.
Any automotive wholesaler has "CHOKE CABLES" that can be cut to length for this to modify the control, but you will now have an independent control.
You don't show a picture of your control, but I believe they are standard on the 70 -80 Chrysler products, more specific, VANS.