OK Automatic Heater Control Experts....Tell Me

Jtt84911 · Jtt84911's Garage

Doing bunch of Winter projects...change 915 gear oil, install Coupler Whisper bushings etc etc. and since the console/shifter were out...I removed the automatic heat system to open it up and change the small light bulb that lights the temp dial (bulb's only been out for only 5 years)

Slid the temp selector knob off and saw this screw and YES of course I turned the screw to see if it moved... and NO.... I have no idea what the screw does !!

It rotates completely independent of the the "clicked" selector so I'm guessing it may used to set the temperature calibration??? Or maybe it controls how much the small arm pulls the two heater cables the open the heater boxes???

What does the screw adjust??

Thanks,
JT

Caledonian · Caledonian's Garage

I'm no expert but here are some pics that may help answer your question.

Old 911 with new owner

wwest · wwest's Garage

Look to me a lot like the type of adjustment that is done to make an electric oven control knob marker point to the actual regulated temperature.

Calibration: "5" should equal a cabin setpoint temperature of "NN" (72dF..??).

86 911 Targa · 03-20-2015, 03:38 PM

Quote:

Originally Posted by Jtt84911

Doing bunch of Winter projects...change 915 gear oil, install Coupler Whisper bushings etc etc. and since the console/shifter were out...I removed the automatic heat system to open it up and change the small light bulb that lights the temp dial (bulb's only been out for only 5 years)

Slid the temp selector knob off and saw this screw and YES of course I turned the screw to see if it moved... and NO.... I have no idea what the screw does !!

It rotates completely independent of the the "clicked" selector so I'm guessing it may used to set the temperature calibration??? Or maybe it controls how much the small arm pulls the two heater cables the open the heater boxes???

What does the screw adjust??

Thanks,
JT

Cabin temp calibration.

After setting the temp switch to 5, hold the shaft, and turn the screw to read 950 Ohms at the potentiometer contacts.

Page 806-7 of the Bentley.

G.

tomphot · 03-20-2015, 03:46 PM

Sigh - I wish I could just get my auto heat to work. It's either All on high heat or totally off. At least in Atlanta it's not that big a deal.

86 911 Targa · 03-20-2015, 04:53 PM

Quote:

Originally Posted by tomphot

Sigh - I wish I could just get my auto heat to work. It's either All on high heat or totally off. At least in Atlanta it's not that big a deal.

Lots of threads on auto heat.

tirwin · tirwin's Garage

Quote:

Originally Posted by tomphot

Sigh - I wish I could just get my auto heat to work. It's either All on high heat or totally off. At least in Atlanta it's not that big a deal.

The most likely reason is there is a thermistor in the rubber nipple that hangs above the rearview mirror. Either it has wiggled loose from the wire or the thermistor is bad.

Jtt84911 · Jtt84911's Garage

wwest and 86 911 Targa _

THANKS GUYS - thought that's what it was.... but had no idea about the 5 setting for calibration!!

tomphot- tirwin is right,,,, there's lots of posts, If you start reading and checking you will definitely get it working. First step is determining if it's a mechanical or electrical issue. For example when you turn the knob to 7 for example do you hear the servo motor inside the control box running and then stop?? The rod that pull the cables which starts a chain reaction of a of other things.... may have popped off on one of the ends. (which you need to do BTW to remove the unit) There's two snap-in covers on both sides on the control unit. pop one off an look inside with a work light and see if the connecting rod is on. If not... and the black plastic socket connectors are OK....pop it back on. If its that issue....that's a 1 minute fix and the difference of the thing working or not working!!!

JT

356911930 · 356911930's Garage

Quote: {The most likely reason is there is a thermistor in the rubber nipple that hangs above the rearview mirror. Either it has wiggled loose from the wire or the thermistor is bad. }

Can you still buy the thermistor or are they NLA?

Rahl

tirwin · tirwin's Garage

They can be bought. I think there is some marking on it that identifies it. Seems like there is an autoheat thread that covers it. There is a test procedure for it.

javadog · 03-20-2015, 07:53 PM

An '86 will have a different cabin sensor, in the lower dash.

FWIW...

JR

86 911 Targa · 03-20-2015, 09:03 PM

Quote:

Originally Posted by tirwin

They can be bought. I think there is some marking on it that identifies it. Seems like there is an autoheat thread that covers it. There is a test procedure for it.

^^^^^
Thermistor

^^^^^
Coupler

86 911 Targa · 03-20-2015, 09:05 PM

Quote:

Originally Posted by tomphot

Sigh - I wish I could just get my auto heat to work. It's either All on high heat or totally off. At least in Atlanta it's not that big a deal.

Read my post.

tomphot · 04:10 AM

Years ago when I bought the car, I fixed the coupler which was broken. That got the system to at least turn on and off. In addition, before I started reading Pelican, I noticed that little rubber thing up by rear view mirror which I thought was an old cell phone microphone

. I undid the screws, gave it few yanks and decided to leave it alone and reattached it. If it wasn't broken before I started, I'm sure I finished it off. I need to fix it properly.