External temp sensor
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Burning Brakes
Joined: Oct 2006
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From: Bakersfield, Ca.
External temp sensor
Would an external temp sensor from a 944 or a 924 work on a 928 of the same year ('83 per say)? If they have one, I would have to think they are very similar.
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From: Southern Alberta, Canada
The 928 ext. temp sensor is mounted in the hose that leads to the alternator. As the alt. spins it pulls air over the sensor and sends the resultant electrical output to the HVAC sensor string. As the air temp increases so the resistance of the sensor decreases and vice versa.
The 928 sensor has a 928 part# so you may have to replace with a 928 piece if required.
The 928 sensor has a 928 part# so you may have to replace with a 928 piece if required.
Burning Brakes
Joined: May 2001
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Are you referring to the external ambient temperature sensor that is fitted into your rear vision mirror giving you the ambient air temperature or are you referring to the external ambient air temperature sensor fitted into the HVAC circuit as Malcolm described?
Tails 1990 928 S4 Auto
Tails 1990 928 S4 Auto
Thread Starter
Burning Brakes
Joined: Oct 2006
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From: Bakersfield, Ca.
the external ambient air temperature sensor fitted into the HVAC circuit as Malcolm described?
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From: Southern Alberta, Canada
If you know what it does have you confirmed its not functional?
Easy test is to remove the LH of the centre console trim, locate the device with the yellow wires, unhook the wires and test the resistance. If the resistance is between 800 - 400k ohms temp dependant on temp. you should remove the LH front wheel and inner wheel trim take the wifes hairdryer in the alt. hose and see how the hot air effects the same resistance checks.........the hotter the air the lower the resistance.
If it doesn't function replace the thermister in the sensor OR spend $103 on the one 928 Int have listed.
Easy test is to remove the LH of the centre console trim, locate the device with the yellow wires, unhook the wires and test the resistance. If the resistance is between 800 - 400k ohms temp dependant on temp. you should remove the LH front wheel and inner wheel trim take the wifes hairdryer in the alt. hose and see how the hot air effects the same resistance checks.........the hotter the air the lower the resistance.
If it doesn't function replace the thermister in the sensor OR spend $103 on the one 928 Int have listed.
Last edited by the flyin' scotsman; Sep 7, 2008 at 11:30 PM.
Thread Starter
Burning Brakes
Joined: Oct 2006
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From: Bakersfield, Ca.
If it doesn't function replace the thermister in the sensor OR spend $103 on the one 928 Int have listed.
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From: Southern Alberta, Canada
ah...........perhaps that small detail should have been revealed at the start as testing an absent sensor is rather redundant.
928 INTL do list a used sensor $95 and 928 Spec list new for somewhat more.
I do have the Parts and Tech Ref Catalogue for 924, 944 and 928 1977- 1988 MYs...........I'll expand the research.
928 INTL do list a used sensor $95 and 928 Spec list new for somewhat more.
I do have the Parts and Tech Ref Catalogue for 924, 944 and 928 1977- 1988 MYs...........I'll expand the research.
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Racer
Joined: Aug 2008
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From: La Pallu, France
Mine was missing also - rather than spending $90+ dollars I bought one of the 300R thermistors listed here for a few pence http://www.rapidonline.com/productin...catRef=61-0405
I mounted the thermistor on a small board inside a drilled tube and fitted it inside the front airdam. Two wires to connect to the original plug and the system now works perfectly.
I'm based in the UK but I am sure you can easily find a 300R NTC thermistor in the States.
Last edited by heliflyer; Sep 8, 2008 at 08:24 AM.
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Joined: Oct 2004
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From: Southern Alberta, Canada
Excellent impro Jay..........another thought for a tube could be a small section of plastic pipe giving the lightness and rigidity required.
I did find the 944 sensor..............totally different.
BTW Jay..............not much room to open her up on Skye but beautiful roads................I recall my visits to Armadale fondly.
I did find the 944 sensor..............totally different.
BTW Jay..............not much room to open her up on Skye but beautiful roads................I recall my visits to Armadale fondly.
Thread Starter
Burning Brakes
Joined: Oct 2006
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From: Bakersfield, Ca.
Hi,
Mine was missing also - rather than spending $90+ dollars I bought one of the 300R thermistors listed here for a few pence http://www.rapidonline.com/productin...catRef=61-0405
I mounted the thermistor on a small board inside a drilled tube and fitted it inside the front airdam. Two wires to connect to the original plug and the system now works perfectly.
I'm based in the UK but I am sure you can easily find a 300R NTC thermistor in the States.
Mine was missing also - rather than spending $90+ dollars I bought one of the 300R thermistors listed here for a few pence http://www.rapidonline.com/productin...catRef=61-0405
I mounted the thermistor on a small board inside a drilled tube and fitted it inside the front airdam. Two wires to connect to the original plug and the system now works perfectly.
I'm based in the UK but I am sure you can easily find a 300R NTC thermistor in the States.
I have found a few thermistor's on line as well. I not sure if they are even automotive related, but I would have to think it would still work.
I did find the 944 sensor..............totally different.
Thanks for the info guys. That's good stuff!!
I'm going to check 928 Intl. and 928 Spec. again. It was just a thought. Thanks again people. 
Electron Wrangler
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From: Phoenix AZ
I have no idea why you would use a 300R thermistor... the nominal 0C value of the sensor is 993 ohms.
This is an NTC (so that's correct) - the specs are:
993 ohms @ 0C
588 ohms @ 20C
457 ohms @ 30C
So overall in the range of ~18 ohms variation per degree
(however these sensors aren't linear)
Based on the specs you will be substantially off with your 300R part at all temps... the temperature variation is in the order of 7 ohms per degree - way too little plus the resistance is way too low - lower than the minimum sensor spec in all cases...?
The 1K NTC on that site is a little better match at 25 ohms/degree... but you'd still need some better adaptation with a parallel & series resistor network. Parallel to reducte the range & series to set the min resistance.
Alan
This is an NTC (so that's correct) - the specs are:
993 ohms @ 0C
588 ohms @ 20C
457 ohms @ 30C
So overall in the range of ~18 ohms variation per degree
(however these sensors aren't linear)
Based on the specs you will be substantially off with your 300R part at all temps... the temperature variation is in the order of 7 ohms per degree - way too little plus the resistance is way too low - lower than the minimum sensor spec in all cases...?
The 1K NTC on that site is a little better match at 25 ohms/degree... but you'd still need some better adaptation with a parallel & series resistor network. Parallel to reducte the range & series to set the min resistance.
Alan
Racer
Joined: Nov 2002
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From: Sproat Lake
I've got one in the air tube right here. pjager@jageng.com Also lots of other parts on clear-out as well. Check out the classified ads. Looking to empty our Bell road shop area (engine, body parts, suspension, rebuilt A/T etc.)
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From: Southern Alberta, Canada
Would you know what tolernace % is acceptable to these resistance values...............i'm currrently reading 645 ohms @ 16.5C.
hold it, just worked out the 3.5C diff from 20C and the math works; 651 ohms calculated vs 645 ohms measured...............6 ohms is liveable.
hold it, just worked out the 3.5C diff from 20C and the math works; 651 ohms calculated vs 645 ohms measured...............6 ohms is liveable.
Racer
Joined: Aug 2008
Posts: 371
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From: La Pallu, France
Hi Alan,
I am by no means an electronics expert but when I looked at the graphs for the 300R thermistor (the bottom line on the chart on the pdf file) it indicated to me just under 1 Kohm at 0degC and just under 0.5 Kohm at 30 deg C, and the 20 deg C figure is pretty close also. Those figures looked close enough to me to match the original at the top and bottom of the scales so thought I would give it a go. It seems to work fine as my previously non working temp control now works.
I would appreciate any further input you have on this replacement regarding any damage it may do to the system in the long run, otherwise for now I am happy with my working system.
I am by no means an electronics expert but when I looked at the graphs for the 300R thermistor (the bottom line on the chart on the pdf file) it indicated to me just under 1 Kohm at 0degC and just under 0.5 Kohm at 30 deg C, and the 20 deg C figure is pretty close also. Those figures looked close enough to me to match the original at the top and bottom of the scales so thought I would give it a go. It seems to work fine as my previously non working temp control now works.
I would appreciate any further input you have on this replacement regarding any damage it may do to the system in the long run, otherwise for now I am happy with my working system.
