Compatibility between auto heater control units

[logician]

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

[emcon5]

Not an answer to your question, but if it was me, and I was faced with replacing that overpriced Rube-Goldberg contraption, I would try and source a manual setup from an older car. Try Easy in Emeryville or Parts Heaven in Hayward.

Less expensive, less complex, 2 "zones" and probably lighter as well.

Just a thought.
Tom