(Modified from my answer to a similar question)
If your control knob is jammed, you may have an easy fix by simply finding a freeing the lever at the other end of the control cable. Otherwise, you'll probably find that the cable is kinked behind the control knob and it's quite an easy fix to straighten it, once you can get to it.
Check both ends of the cable by first removing your radio and looking up behind the control knob with a torch for one end. The other end is connected to a lever affixed to centre housing to the left of the clutch pedal(Mine's RH drive, so it 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 and possibly a torch 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)!
If you do have a kinked cable, the bad news is you need to first remove the console around gearstick to then get the centre radio console out to carefully straighten the cable just behind where it attaches to the control knob. Apart from a few millimetres of bend to fix it to the plastic arm, the inner cable should be straight. The common fault from forcing the control knob against a stuck flap lever is a nearly ninety degree bend in the inner cable about 2cm behind the control knob which severly restricts teh range of movement.
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(from forcing it when the flap at the other end has stuck after a long period on the cold setting), like mine did, which means it isn't opening the flap enough to let hot air through the system.
The plastic part of the control knob mechanism to which the cable attaches looks very flimsy, so the inner cable will need to be straightened with great care but I managed it last weekend and the fix worked fine(FWIW, I removed the radio console without removing the lower console but this requires some serious twisting of the plastic and you risk breaking the console, or scratching the steering column doing it this way).
Alternatively, if you just wish to bodge the heating full on through the winter, the cable at the lever end can be removed easily. Pull the cable away from the lever towards the clutch pedal(It should just pop out of the lever) and then come up with a way of sticking the lever in the warm position(it naturally springs back to cold).
Bearcub, November 2008
