The resistors control the speed of the blower. The heat is controlled by a flap that lets air flow through the heater matrix. The flap is adjusted by a cable that is pulled and pushed when the heater control knob is turned. It is likely the problem has been caused by a loose spring clip that usually holds the cable in place. On my Tino the spring clip had broken free of the plastic and could not be refitted securely. I fixed it by drilling three small holes and fitting 2 cable ties - one diagonally across the spring clip, and one across the cable over its endstop. I did the same for the air direction cable which was also loose with two cable ties diagonally across the springclip.
To see if this is the fault you can lever out the oddments shelf above the ashtray and look at the cables as you turn the knobs. If the black outer part of the cable moves at all it is loose and needs to be securely re-fixed. It is also possible the inner cable has kinked and won't push back in until straightened.
To get proper access to these cables you need a Phillips screwdriver. Remove in this order: Panel beneath the steering wheel (easy, just 3 screws); Glove box (loosen trim near base of passenger door to get to one screw, also remove the hinge pins by pulling them sideways to get the glovebox door off); plastic surround around the heater controls (3 screws, one underneath a pop out plastic infill) and finally the big central panel with the ashtray in. Disconnect the cigarette lighter as you remove it.
If all that sounds too difficult the quick fix is to reach up to the left above the clutch pedal behind the center console and feel where the cable meets the heater matrix air flap. Prise the oddments shelf out first and look through to see what you are doing and where the cable goes to. Move it down towards the engine to reduce heat.
James, December 2008
