Heater not working correctly

Hi All Looking for a little help my 1991 940s heater is only working on warm when I turn the dial it does not get colder or hotter! With my limited knowkedge I have pulled off the control knob and everything behind it turns as it should but the temp does not adjust. The knob does seem to turn easy and freely. Anyone any idea where to look next. Thanks and best regards.

Heater 

Hi Boneshaker Try looking at the control valve around the clutch pedal area from the inside. It will have two pipes going to the left of the car and a cable which comes down from the control knob on the dash. Turn the knob and see if the arm moves. This regulates the water flow. Maybe the cable has come adrift or the arm is broken or the valve has siezed. Hope this helps.... Rgds Mike

Thanks Mike J I will have a look at this at the week-end and let you know how I get on. Thanks Again

Had a look tonight what is happening is if I grip the outer black cable the inner cable operates perfect as soon as I let go of the cable and turn the control the whole thing moves thus not adjusting down at the pedals hence no change in heat. I found a small white plastic block that looks like it should be fitted somewhere to stop the outer cable moving. Any ideas where the block should fit and where/how the outer cable should be secured. At least I can move it manually I might have to have summer and winter settings!!!!!!!! Any ideas welcome. Regards

Whole cable should be clipped onto water valve. There is small rectangular hole on the rectangular part of valve. There should be either small steel or plastic clip that holds the cable against the hole and outer edge of part. It's just quite hard to secure it properly, since it's not very accessible.

Thanks Tom 85 going to show my ignorance and ask where the water valve is? I have the small plastic clip, is it by the two hoses on the floor or up behind the control. Many Thanks again your advice is really valuable especially to a novice like myself. Best Regards

Control/water/heater valve is same thing. It's the part that you already noticed just little higher than the clutch pedal with one hose getting out of it to heater. The picture in attachment should give you idea (the fixation of cable is visible). I'm speaking about 700 series, but there should be very little or no difference.

Hi All I have had a look this morning the cable seems to be well secure down at the pedals my car is an auto so no clutch. The problem seems to be that the movement is coming from the top end by the control knob I do have a white plastic cable clip spare!!! not sure where it has come from. If I grip the outer cable lightly at the back of control inner cable works perfect. Should it secure to the back of the knob?? Thanks in anticipation.