Auto heat controller sensors
 

Guys been investigating the Auto heat controller on my 1979 911 Targa and have discovered that there is two sensors that are not connected, does anyone know what they do are were they are situated
Jeff

There is heat sensor (thermistor) in one of the heater valves that control hot air entering the cabin from the heat exchangers. There is an interior heat sensor located in the overhead above the rear view mirror on coupes, not sure if it is there on a Targa. The auto heat controller regulates how much the heater valves open/close based on the desired temperature setting, the temperature of the hot air from the heat exchangers and the inside temperature. These sensors are no longer available, but can be substituted with thermistors from electronics part houses.

The Plugs are there but having traced the wires the sensors have been cut off , the temperature dial seems to work as it drives the connecting rod depending on the setting backwards and forwards this opens and closes the metal valves in the heater line , knowing that the dial operates the vales, why would the sensors be needed , or do the override the manual controller?

The cabin temp sensor in the Targa is in the dash to the right of the steering wheel (circular louver).

The sensors are nice b/c they close the loop with the controller, so when the temp is reached, the controller will actively regulate the temp' by driving the heater flappers.

Here's one thread on the subject.http://forums.pelicanparts.com/porsche-911-technical-forum/639062-autoheat-troubleshooting-4.html

Jeff,

Are the sensors still in place and the wiring has been cut, or are the sensors and wiring missing?

Here are a couple of thermistor P/N's I compiled from reading threads about the autoheat controller:

NTC thermistor interior; B57891M152J

NTC thermistor heat exchange; AL03006-1576-101-K

If the housings that the thermistors were mounted in are in tact, you may be able to rewire them. I have not had to replace my sensors so I am not sure these thermistors will fit in the mounting location.

the cabin sensor, located in the dash with a little fan on my86 930, of course monitors inside temp to regulate the heat based on the dial setting.

the one in the heater box, I assume, is there so that the heat does not come on until the engine/air is hot.

I just turn the dial u or down as needed so I could care less about the temp sensors.

If the heater valve sensor is there but not working you can rebuild it for less than $5.00.
Do a title search for caloric feeler.
if it’s missing Porsche wants $$$$


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Guys sorry for late reply I thought the sensor wires had been cut but they havnt I have tried tracing the internal one with much difficulty it is a single white wire that disappears behind the dashboard . And I can't locate the sensor I don't have a circular vent next to the steering wheel, will continue the search today

Thanks for the thermostat info

Guys still struggling to find the internal auto heat sensor
Anyone know were the temp sensor for a 1979 sc Targa
Is situated.