On my bus the heater valve, which is accessed by removing the spare  tire,
 moved very stiffly because of age. I cleaned it with maybe brake  clean and
worked it till the movement was free. Then I dried it and all. Then  greased
it up to assure free movement.

In the meantime, becaus eit was stiff, the haeter valve control cable had
bent up at the dash board end. I was able to straight it and it's still in use.
I hit each end with a little grease--silicone grease would be a good  choice.

Good luck
Jeff
83.5 westy
LA,CA

In a message dated 5/23/2005 12:03:14 PM Pacific Standard Time,
icebox500@GMAIL.COM writes:

My front  heater is always on... I assume then that this is because the cable
that  controls the valve in the diagram is either broken, bent, or  weak.