9two8

I recently located this sensor tied to the inner fender support, but could,nt find any cooling hose or bracketry to fix it to, so I mounted it in the top of the brake cooling duct and it works ok,... drilled a tight-ish fit hole and it sticks down about an inch or so.

Ken
80 928s
Manual

Alan

The ext temp sensor specs are:

993 ohms at 0 degrees C (32 degrees F)
588 ohms at 20 degrees C (68 degrees F)
457 ohms at 30 degrees C (86 degrees F)

it is just a thermistor and reistor network - you could approximate with standard components... better than a fixed resistor - but I'm sure you can find used if you look hard enough. Try 20th street - a rennlist sponsor.

Alan

Manfred

Hey all, just for clarification, if I'm getting an accurate outside temp reading on my dash, does that mean this sensor is functioning normally? In my situation the AC only comes on when the slider is all the way to the left but I am getting a normal outside temp reading on my display. Is checking this sensor still my first step or should I be looking at the sensor behind the console?
Thanks,
Dan

j.kenzie@sbcglobal.net

No. The digital dash temp sensor is independent and located in the side view mirror IIRC. The HVAC sensor is under the driver's front wheel well. Alsoyou need an unbroken component chain from outside temp sensor to HVAC head unit to inside temp sensor, for correct function.

Emickelsen

Thanks for the reply. Mounting it is the easy part, i'm not worried 'bout that part. Finding one is the trick. Did the OB's use a special one or something? I would have to think one from just about any year, or even one from another model (944, 924) should work.

Fogey1

I googled "buy thermistor" and found a lot of sources. I didn't go further because mine works.

Emickelsen

Good input Fogey1! I never thought of that.

Would something like this really work? Seems almost to simple, and there are lots to choose from.

http://www.omega.com/ppt/pptsc.asp?ref=AD590&Nav=temd10

SeanR

Here's an odd one.

Outside temp sensor is good, circuit is good. Car is full hot off of the full cold slider setting.

Checking resistance at outside temp sensor it shows 544 and changes with temp change up and down.

Check resistance at plug 2, pins 4 and 12. Key on, slider full cold shows 340 kohm. Move the slider all the way hot, shows the same 340 kohms. No changes with from any position on temp slider.

Thoughts? Bad HVAC head unit?

Herman K

I have a head unit that I have taken apart it needs a new relay I think the inside boards are good let me know if you can use them for testing your unit?

SeanR

Thanks Herman,

I've got a rebuilt head unit here (relay wise) in the middle of testing the control switch now. The A/C switching works great I'm just trying to diagnose the full hot/cold issue. Apparently there is a pot inside the head unit that helps control this stuff.

SeanR

Ok, tested the head unit, power is all good at all the connections at the 15 pin connector.

I just ohm'd out pin 13 and 14. Test range should be 0-1000 ohms. This one goes from 3-562 with no variation along the slider. Very odd.

SeanR

Testing my 'test unit' and it ohm'd out at a range of 800, not perfect but better than this one.

Installed in the car and the test on Plug 2, pins 4 and 12 went from 4.75 down to 4.01. Much better. So, from this I can guess that the potentiometer (spelling) in head unit one is bad. Learn something new every day with these cars.

Hope this helps others.

Mrmerlin

Sean did you try to test the outside sensor from the connection at the HVAC head?
there is a possibility that the plug connector on the car side of the harness isnt making contact. I know you found the bad potentiometer but still worth investigating. good luck

SeanR

Temp sensors are all good. The potentiometer not varying the ohms is causing the lack of mixing of hot and cold. That was my first test was from the plug number 2 on the mixing motor. If that circuit is bad you will know right from there. It gave me an odd reading, it should have a range when you move the slider, so I pulled the outside sensor and tested it. Good readings. I had no idea until later in the testing that there was a Pot in the head unit.



Once I went through the WSM testing, the last test was the head unit ohms and bingo, that was the issue. When testing it, you pull it out of the car so it is isolated.

UKKid35

Thank you very much for this tip, just wish I'd read it before my first attempt. On my second visit the headlight route made life much much easier.