I'm sure everyone is familiar with the controls, but mine has the dual 'vertical dials' between the shifter and radio. The drivers side wheel turns with more pressure than it should take, but the passenger side doesn't move at all. Is it supposed to?
Both of them should move relatively easily. Keep in mind that both of them are connected to cables as well as vacuum switches. Chances are that the one that doesn't move has a frozen cable. The cable on the right one controls the 'deicer' door down in the plenum. The cable on the left one controls the heater temp control door (also in the plenum).