Automatic heater control unit repaired -- 70 cents!

[rokemester]

This spec is the same as the thermistor in the heat exchanger. Can I use the same thermistor?

[86 911 Targa]

Originally Posted by rokemester

This spec is the same as the thermistor in the heat exchanger. Can I use the same thermistor?

I think the heat exchanger sensor is 1.7K Ohms @ 20C/68F.

[douglas bray]

I am backdating my heat and would like to remove my perfectly good autoheat module from between the seats without harming it.

Can I simply unplug all the wires at the module?

.....or will I have to chase wires under the carpet? I don't want to do anything but unplug it and tuck wires away. Can this be done?

[tirwin]

Douglas,

I thought about doing the same thing a couple of years ago and I looked into it. I'm trying to remember all the details. One difference is the servo motor on the autoheat only connects to one lever that adjusts both of the flapper boxes. If you plan on replacing it with dual levers then you will need to think about whether you want to make both levers work or whether you can just have one lever control both. You'd need to source the levers of course. As far as the wiring there is a wire that goes to the thermistor in the ceiling -- you obviously won't need that. There is a wire (and a ground?) for the lights in the autoheat unit that come on with the dash lights -- I think it's black with a blue stripe. You can tape that off. Then there are maybe a couple of wires (yellow?) that are power to the servo motor/control board. You won't need those either. I can't think of anything else in there you'd need to keep.

[douglas bray]

Thank you,

Finally getting some time to work on this.

I've got the manual levers with the later version wire clips like pictured below,

I've got the manual cables ready to install with the correct ends and the rubber boot that goes over it.

The driver's side lever and flapper box will work as the window defroster. Initial testing leads me to believe I may need to put that footwell blower back in.

The passenger side lever and flapper box will provide heat to the passenger side feet. There will simply be a 180* bend in the ducting as it exits the footwell. I live in SoCal and have never used the heat so....my wife may someday want to warm her feet.

I've got the backdated flapper boxes and fresh orange ducting already installed.

Tomorrow the passenger seat comes out and she goes back up on blocks and the brake cables come off to swap out the brake lever and manual pulls.

Similar to this:


Should end up looking like this:



Underhood ducting can be seen here: Rennlist Discussion Forums - View Single Post - A bit of an update

I've removed the fresh air blower, box, and controls. The controls that were in the center console (also deleted) will be in the space the fresh air controls used to be.

Car is on a serious diet.

[Bill Douglas]

Well done. Mine is in the attic somewhere and I cut a hole in the top of the housing to use as a coffee cup holder. Call me old fashioned but I just pull the lever up for hot air.

[douglas bray]

Done. A perfectly good and working autoheat has been deleted.

[rokemester]

Well I've made some progress with my autoheat system. I bought a used controller and did some further swapping of components between "new" and original controller. When I turn the knob to the first position the control arm goes to the wide open limit. The fan speeds don't seem to change much until I turn all the way to the full defrost position. I replaced the temp sensor in the exhaust system. Could it be an issue with the interior temp sensor? Thanks.

[rokemester]

Can anyone verify that this is the OEM thermistor set up in Porsche part no. 911.624.065.00? It looks to be a 2.2kOhm thermistor with a 6.6kOhm resistor in parallel.

[rokemester]

...Can someone with a working autoheat controller explain how the controller is supposed to behave normally? For example in position 3, does the control actuator move to a partially open position in the heat valves (flapper boxes) and stay there? Or does the actuator move to a position and cycle back and forth a bit depending on cabin temperature? I've never had mine working properly and wondering how it's supposed to work when functioning properly. Thanks.

[76carrera3.0]

Roke, My car is a very early '76 with auto heat so it was basically a new option at the time and the actuator moves to a position and then cycles back and forth depending on the cabin temp. If I set the control knob to position 10 the lever is full up all the time and does not cycle at all. Any other position then 10 on the dial and it will move to some partially open state and oscillate as it tries to adjust to maintain a constant cabin temp

Hope that helps some

[rokemester]

Yes that helps!! I thought that I saw from a previous thread that this is how the system is supposed to operate but needed to verify. Thanks, it makes sense that the controller moves the flaps open and closed to maintain whatever temp the position 1-9 dial indicates.