Estima Heater Problem

[AbingdonPhil 0]

I have a 1992 Estima Emina diesel. The heater only provides lukewarm heat when set on maximum (but cold when set on cold). I have done all the usual checks - heater matrix ok with both pipes hot when valve open, no water loss or overheating problems etc - and concluded that the problem is with the air blender flap and most likely the outer cable has slipped. I can get at the top end by the controls and can see that both the water valve cable and the air blender cable are properly seated. However, I have no idea where the other end of the air-blend cable terminates - I certainly can't see it under the bonnet. Can anyone help please? Many thanks