What does the Heat exchanger temperature sensor control ?

[Bigdog1758]

Hello, I have a 83 911 SC and the heat is...well...poo. I do NOT have a automatic heat switch, no footwell blowers, nor any type of sensor in the car near the rearview mirror or anywhere else (I've been researching this for two days). So, what the heck does the heat exchanger temperature sensor control.....control, if anything? Rear engine compartment blower works off the heater switch on emergency brake. Bentley doesn't mention it. Oh, and the heat exchanger valves open and shut like a charm. Thanks!

[wwest]

The automatic heat control system has a servomotor that adjust the heat level flowing from the heat exchangers instead of the 2 manual levers.

[scarceller]

Where is this sensor located? On the heat exchanger? Pic?

[wwest]

Porsche 911 heating systems - Philip Raby Porsche

http://members.rennlist.com/imcarthur/heatcomponents.htm

[wwest]

Originally Posted by scarceller

Where is this sensor located? On the heat exchanger? Pic?

2 sensors, one in the duct under the car just forward of the heat control flapper valves, the second either between the sun visors or in the dash above the ash tray depending on the MY.

[KTL]

The sensor is basically riveted to heat "flapper box" that the heat exchangers are connected to. It's #11 in the diagram and called a "caloric feeler"

[scarceller]

Originally Posted by wwest

2 sensors, one in the duct under the car just forward of the heat control flapper valves, the second either between the sun visors or in the dash above the ash tray depending on the MY.

I assume you only have these sensors if you have auto heat control?
Could someone have replaced the flapper box and it came with a sensor from an Auto Heat 911? Is that possible?

[wwest]

Originally Posted by KTL

The sensor is basically riveted to heat "flapper box" that the heat exchangers are connected to. It's #11 in the diagram and called a "caloric feeler"

That's the sensor that the system uses to determine if the airflow from the heat exchangers is warm/hot enough to warrant routing it to the cabin.

The second sensor, either between the sun visors or in the dash, is used to modulate(***) the level of heated air flowing into the cabin in order to control the cabin atmosphere temperature level in accordance with the setpoint.

*** Servomotor moves the position of the flapper box vane position.

[scarceller]

But the OP is wondering why he has the sensor on the flapper box but he does not have auto heat?

[KTL]

Originally Posted by wwest

That's the sensor that the system uses to determine if the airflow from the heat exchangers is warm/hot enough to warrant routing it to the cabin.

The second sensor, either between the sun visors or in the dash, is used to modulate(***) the level of heated air flowing into the cabin in order to control the cabin atmosphere temperature level in accordance with the setpoint.

*** Servomotor moves the position of the flapper box vane position.

I simply posted a picture of the sensor that is connected to the heat exchanger piping and made no mention whatsoever as to the sensor's function.

[Bigdog1758]

I have the sensor with wire on the driver's side flapper box only. I do not have automatic heat nor other sensors inside the car. The car is 33 years old, and has had its share of owners, so who can say if what it originally had. I might feel brave tomorrow and try to trace the sensor wire out, if its possible. Should go through the shift tunnel, I imagine. Thanks for the input everyone.

[Tremelune]

Originally Posted by Bigdog1758

I have the sensor with wire on the driver's side flapper box only. I do not have automatic heat nor other sensors inside the car. The car is 33 years old, and has had its share of owners, so who can say if what it originally had. I might feel brave tomorrow and try to trace the sensor wire out, if its possible. Should go through the shift tunnel, I imagine. Thanks for the input everyone.

Sounds like something was replaced. The wire you describe is the sensor for auto-heat. It is common for people to remove auto-heat, as it was not a great implementation. It is also common for people to replace flapper boxes because they rust out, though it would be strange for someone to retain the auto-heat attachments.

[SilverWT]

Originally Posted by Bigdog1758

so who can say if what it originally had.

If we are talking about an '83 SC (as listed under your "Garage") it would have originaly had automatic heat, unless it is a Cabriolet.

It would have had the sensor you see near the flapper box and a sensor between the sun visors (9 in the diagram posted above). It would have also had the black control box between the seats with a dial with positions from 0 to 9 plus DEF (the Cabriolet had a black box with a dial from 0 to 3). The single "emergency" manual heating leaver present in earlier automatic heat control boxes was deleted for '83 (the Cabriolet had two manual leavers).

Mark

[javadog]

Originally Posted by SilverWT

If we are talking about an '83 SC (as listed under your "Garage") it would have originaly had automatic heat, unless it is a Cabriolet.

Automatic heat was an option, not standard.

Originally Posted by Tremelune

Sounds like something was replaced. The wire you describe is the sensor for auto-heat. It is common for people to remove auto-heat, as it was not a great implementation. It is also common for people to replace flapper boxes because they rust out, though it would be strange for someone to retain the auto-heat attachments.

If the car originally had autoheat, there should be evidence of the interior sensor having been there in the headliner, unless the headliner has been replaced.

If the flapper valve on the left side has been replaced, it would be unlikely that they would have routed the sensor wire into the car, so that may be a clue. Removing the sensor will leave some holes in the flapper box, so that it may have been easier just to leave the sensor in place, if in fact the flapper box has been changed.

JR

[SilverWT]

Originally Posted by javadog

Automatic heat was an option, not standard.

Ah, hadn't realised it was still an option in the US, standard in the UK.

Mark