There are 3 bowden type heater cables that manually move levers to control the heater.
The 2 main cables terminate in the right hand footwell.
In Right Hand Drive cars, the cables are sometimes covered although some early RHD cars didn't have a cover.
These cars sometimes had issues with floor mats getting in the way of the lower lever.
If this happens, the heat controller lever won't move all the way over.
On Left Hand Drive cars, the levers are covered the carpet and the polystyrene footwell block.
3 of the levers are attached to bowden cables...
...the "direction control lever"...
...the "heat control lever"...
...and the lever that selects either fresh or recirculated air.