I have an old Kelvinator double door (up and under) freezer with superfreeze facility and all controls situated above top door. The temperature setting (extreme right hand) runs through the top of the freezer to the back where the thermostat is situated. The axle of this control is stuck ( I have proved it by removing the thermostat and then trying to turn the control in front on the freezer. How do I "unstuck" the shaft of the control?