Hopefully you'll find that the cable is kinked behind the control knob.
Bad news is you need to first remove the console around gearstick to get centre console out to carefully straighten the cable.
You can check both ends of the cable by first removing your radio and looking up behind control knob with a torch for one end. Other end is connected to a lever affixed to centre housing to the left(and above) of the clutch pedal(Mine's RH drive, so may be on passenger side in LHD). Shouldn't be hard to spot although you'll need to have your head in the floor well to see it!
Make sure this lever isn't jammed, or any fix will be very temporary(try and use your other hand to move control knob at the same time as one hand moves the lever to avoid possibility of further damage, or kinking)!
Alternatively, if you wish to bodge the heating full on, the cable at the lever end can be removed easily. Pull it away from the lever towards the clutch pedal(It should just unclip) and then come up with a way of sticking the lever in the warm position(it naturally springs back to cold).
Anyway, I'm reasonably certain that you'll find the inner wire of your control cable has simply developed a nasty kink behind the control knob, like mine did, which means it isn't opening the flap enough to let hot air through the system.
The plastic cable attachment to the control knob looks very flimsy, so the inner cable will need to be straightened with great care but I managed it yesterday and the fix worked fine.
Bearcub, November 2008
