What would cause the temp. selector to be either be full on heat with even the slightest movement of the slide button and totally off in the off position. I have a newer hot water heater valve and I think that is functioning properly. I might add that the a/C doesn't work at all and I'm getting ready to sort that system out. I do have the HVAC controller out because I'm putting a new sunroof switch in..so is there something to check with that? Thanks, Doug.

 

The output temp of the system is controlled by a motorized control box that is controlled by the total resistance of a string composed of:
- Outside temp sensor. (Most likely cause. The sensor is located in the alternator cooling hose, in the left front wheel well, under the headlight. The wiring gets damaged...)
- Inside temp sensor, located behind the little grille in the face of the dash on the passenger side (LHD).
- Temp Control Lever.

If this string gets disconnected or damaged, you will have zero heat when the lever is full cold, full heat if the lever is barely moved from the full cold position.

 

Thanks Wally, the inside temp sensor is newer, so I'm going to replace the outside sensor. Thanks ,Doug.