Heater control jammed on hot

Check against the bulkhead, near the middle of the vehicle, see if there is a valve with a cable attached to it. If so, move the heat control lever and see if the lever on the valve moves. If so, replace the heater control valve.

If the heater works by using vacuum to move a blend door, carefully remove the plastic dash bezel piece and the heater control. Move the temperature lever and follow it to the air box. Verify that all control rods, levers and gears move properly. Make sure that the required vacuum is getting to the control valves in or on the air box behind the dash bezel.

I'm not finding a reference to the 200 Galaxie in my reference material, so it must be a Europe only vehicle. My best suggestion would be to find a repair manual such as a Chilton's or Haynes (or the equivalent in Europe). They are relatively cheap, usually around $20US or less.