Pelican Parts Forums - Compatibility between auto heater control units

Hi,

The automatic heater control unit in my '86 930 seems to not be functioning. The symptom is that the servo that opens the heater vent does not operate. I have checked the resistance on the two temperature sensors (cabin and heat exchanger) and they both seem within specifications, so I don't think it is a problem with those. I have also checked to make sure that the unit has power, and it does. So I have come to the conclusion that the circuit board within the control unit is burned out.

So, I would like to replace the heater control unit (part 930.659.059.01) with a functional used one. A new unit costs $1100, so I would prefer to find a cheaper solution. Unfortunately, it seems that the '86 Turbo control units have a different part number than the control units from Carrera models of similar vintage, and it looks unlikely that I would find a control unit for exactly an '86 Turbo. I was warned by someone once that they burnt out their wiring harness using a different automatic control unit. However, looking at the wiring diagrams, and studying the part, it doesn't seem obvious why another unit might cause such a serious problem. All of the automatic units of the '84-89 (Carrera/Turbo) vintage seem to be wired the same, and operate the same circuits.

Does anyone have any information or experience about compatibility between automatic heater control unit in Carrera vintage 911/930? I'm not sure about SC vintage, but information about those might also be relevent. Also, if the units are not directly compatible, might the circuit board inside be compatible -- is it possible to swap only the circuit board? Alternately, does anyone know of a good source for rebuilt heater control units that might cost less than $1100. Any help would be greatly appreciated!

-Juan