Hey georges 928S, By cycling - I mean to simply repeat the last movement of the slide control lever. On my car, if I move the temperature control toward the full left (cold) position and the heat sometimes doesn’t shut off - I know to move the temp lever back slightly toward the right and then back to the far left. I suspect that the electrical switching contacts within my console mounted Heat/AC control unit may be a bit worn and sometimes does not complete the vacuum control solenoid circuit properly.
The advice from Mrmerlin and MPDano to start with the hot water control valve mounted on the firewall behind the air cleaner is the best place to start your troubleshooting. This vacuum controlled hot water shut off valve must open/close correctly with no internal hot water leakage or you will never get the rest of your ventilation system to operate satisfactorily. If this valve is defective simply buy a new one.
By the way, Dwaynes Garage Site:
www.dwaynesgarage.norcal928
is an excellent place to find lots of good information and experience on the 928.
Good Luck, Michael
