Auto heat control operation
 

Does the cabin air temp sensor run all the time or should it be off when the console dial setting for heat is zero?


87 911
Thanks

Are you talking about the red circular dial between the two seats ? I've got that red 0-1-2-3 dial on my 87, and in classic Porsche logic the 0 setting is not off but is the lowest "on" position (which I believe other threads confirm). I believe that dial essentially operates the footwell blowers on 0, 1 and 2, and in the 3 position a secondary blower kicks in.

Keep in mind that there are two "automatic" heat controls. One reads 0-3 and the other, like mine, reads 0-10

Yes I am talking about the dial indicator which is part of the auto climate heat control..the dial switch is tied into the temp probe in the heater box and controls the butterfly valve to allow more warm into the car and it also gets feedback from a dash probe... the question is this dash temp sensor probe under the dash ash try which pulls cabin air into it and then it provides feedback to the dial switch. I am trying to find out if this sensor runs continuously or turns off when the dial indicator between the seats is swicthed to Zero.

As you say.. zero is the lowest setting.... then what shunts the currant to this probe to turn it off or dose it run all the time while the ignition system is running .

Do you have the full auto heat climate control system zero through 9 plus defrost? If so could you check to see if you have a small rats cage motor running just behind the ash tray....this is the auto temp semsor for the cars cabin...

Thanks for your reply....

87 930 coupe

I'll check tonight and come back to you tomorrow. I don't have the 0--9, just the 0-1-2-3, so it may be different from yours.

Kurt -- are you a heating system guru ? Coincidentally, my entire heating system stopped working all at once the other day -- silence when I pull up the two red levers. Nothing, nada. Worked great before. I've cleaned out a little dust under the two levers, and the front fuses all look good. It sounds electrical rather than mechanical to me. Think this is probably the heater "relay" (a control module containing relays, actually) in the engine compartment ?

Thanks

If you have the two red levers, you don't have the auto heat. The auto heat box can best be described as a Rube-Goldberg contraption which pulls the heat lever for you. Early models still had the lever, and you can see it move up and down as the servo adjusts the heat level, later versions the exposed portion of the lever was removed.

Tom

"the question is this dash temp sensor probe under the dash ash try which pulls cabin air into it and then it provides feedback to the dial switch."

There're two sensors which are used by the servo controller in the heater unit.
If either of these is "open", you'll have problems. That's the typical source of
problems for the unit. If the cables move with difficulty, that can damage the
motor in the unit.

The operation of the heat settings 1-6 operate with corresponding additional heat delivery.. as the servo only operates the lever and butterfly valve . At settings 7-9 and defrost the additional blower units kick in nicely.. so again is the Air sampling unit in the dash supposed to turn off when the dial setting is at Zero or is it supposed to be on all the time while the ignition is on.. Thanks everyone for your help

All the time judging from mine & the wiring diagram. It is fed directly from #7 Fuse in Fuse Box 1.

Ian

Thank you imcarthur... my interpretation of an electrical diagram showed one of the wires to the air sample sensor going somewhere else for which I didnt have the additional pages to review... based on what docs I had it seemed that the other connections would not have interfered with the currant source so I was hoping that power all the time was its standard MO... thanks again.

and emcon5 you hit it on the head when you said it was rube...ish.

To all thank you for your time..

The operation of this unit is very very simple. The two temp sensors
are always powered with the key "on" as is amplifier/controller board.
As the knob is turned from the off position the internal motor will
start to move the rod. Each position of the knob should result
in a small additional movement of the rod. If the rod moves to
almost the max position, then the controller is bad or the sensors
are open. It's that simple!