I think we are before the days of duovalves and the two temperature knobs are linked directly to water valves ; the direction knob in the middle links mechanically to the various flaps etc ( sometimes the linkage rods can pop out of place , causing something not to work ) .
To remove the control panel ( this is all from memory , being about 15 years since I last had one of these cars ) , you pull the knobs off ( they can be very tight and may need something like a pair of pliers with rubber or cloth in the jaws to avoid damage to the knobs ) but they DO pull straight off . Behind the knobs you will see a small bulb which illuminates them , these just pull out , put them aside so they don't get broken ; also behind the knobs you will find large nuts , undo these . Just above the radio , I think there are two crosshead screws going up into the bottom edge of the heater panel ( you may need to remove the radio to get at these , with them undone , the bottom edge of the panel should pull outwards , then clear the knob spindles , after which the panel can pull downwards and out from the top . There will be various bulbs etc still attached to the rear which can be unplugged ( if any parts of the panel were not illuminating , now is the time to replace any blown lamps ) . With the panel out , you can operate the controls and see what is happening .