Heater Sensor

[markt944]

Am i right in thinking this is the outer air temperature sensor



A reisistance test shows its had it ,its stuck


Thanks Mark

[aj951]

That's it! Sorry it's bad.

[ketchum951]

Can you let me know what cause in your car this stick sensor what problems where you experience ? what is the function of this sensor? how you test sensor , I had a full heat issue in my 951 and want to get it fix, but I don't have experience with electronic or basic mechanics but will love try to solve can you let me know where find sensor how to take out and how test it thanks

[markt944]

Ok thanks i have some thermistors on the way

Basicly the heat in the cabin warms up once thermostat is open ,even though the knob is on max i dont think its as hot as it should be

But after about 5 miles it cools down to much and never seems to get back up!Even though its not freezing air comeing out of vents}


Anyway i have come to the conclusion that mine is stuck at 15 ohm {it should show 10000 ohms at 25c +/- 10 %!!!

As the temp goes up resitance goes down so basicly the computer thinks that the outside temp is hot so its opening the flaps to let more fresh air in ,thus being to cold for time of year {its january and freezing outside}

Now with ur problem it could be that a sensor is stuck the oposite way round causing it to be to hot ,but check those clips first .If the clips are broken by default the heater is designed to go to max heat so u at least dont freeze in the winter

Because i have the opposite to u i did a little test if i disconnect the outer sensors{creating an open ciscuit} thats now basicly telling the compter that the outer temp is freezing ,which it is

And sure enough it now doesnt cool down and gets a lot hotter !,but u have to remember to keep cabin temp at a chosen heat all 3 sensors have to work together to send Right info to computer

I did a test on INTERIOR sensor the other week and that even though it works was not showing the right resistance for a given temp

I have not yet checked MIXEING CHAMBER SENSOR,it more difficult to get at

Any way i have some thermistors on the way about £4 for 4 more than enough i will replace with these first to see how i get on

If u are going to buy Thermistors u need to get the right ones u need ones that have 10 k ohms @25c , but also ones with the right resistance curve


The porsche manual recomends when testing original ones thay should show

34k - 0c
20k -10c
10k -25c
all figures +/-10 % to be within tolernce


Mark

[aj951]

Ketchum951,

A full heat problem can also be caused by an open heater control valve located in the engine compartment. The valve is vacuum operated and controls coolant flow to the heater core. If vacuum to the heater control valve is lost, the valve will stay open and can not control the amount of warm coolant entering the heater core, thus giving full heat. This too is a fail safe so that you have heat if it does fail.

[markt944]

I already checked the vacum side of things on my car a few months back and every thing was ok

Sure enough like u say that could aslo give max heat ,but what u need to remember is everthing is controlled by the computer which in turn gets its info from the sensors

Even if the matrix had hot water flowing through it at all times{like an ordinary car} and the fresh air flaps wer opening as they should it would still cool it down not heat up ,it would only heat up if fresh air flaps are not opening

Get under the dash and turn the hot/cold knob u should see one of the motors operating the plap via a rod whihch is held in place via those clips

Also have tweeked the hot water valve under the bonnet to see if it can actually open/close and that its not seized