Anyone know how these Temp switches work?
 

I posted this in my cold start thread over in the 930 forum, but this would apply to non-turbos and we get more eyes over here.

So, anyone know how these things work?

I pulled the 35c switch out by the breather cover and the 15c switch on the far right of the right side cam chain cover. They are clearly marked, so the one on top is the correct one for the switching on of the solenoid used for advancing timing at cold start to raise the idle. The solenoid never gets power once the engine warms up a bit.

I figured I would pull the 15C one too and compare how they operate and neither seem to do anything...

I tested continuity cold and both are infinity Ohms. I dropped them both in scalding hot water and waited and neither one closed the circuit and neither one has continuity from the lead to the base.

I took a pic of the schematic showing both switches and it seems to me they close when warm at their respective temps, completing the circuit, no?

What am I missing here? They cant both be bad can they?

Anyone got their motor out or have one of these laying around and want to test theirs? SmileWavy

Thanks in advance!

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I don't think they should ever be infinity, or completely open. As they warm up, the resistance changes. I think they are not an open/close switch but rather a thermo resistor.

So as they get warmer, the resistance goes down? I guess the fuel enrichment control unit that this plugs into can measure the resistance to determine the temp and then engage the solenoid when it reaches the correct resistance?

I get nothing but an open circuit on both of them.

neither one controls timing. timing is strictly control by mechanical devices. either weights inside or vacuum.

I don't know why there are 2, but they control fuel.
I think the one on the cam cover is to monitor engine temp to richen up the mixture when cold.
why the one on top, I don't know.
one goes to the fuel enrichment control and the other to the O2 control.

there is another switch on top with 2 vacuum lines going to it. this controls the vacuum to the dist when cold. no electrical connection.

So the 35c one up top engages the solenoid that opens the blue vacuum hose off the distributer, which retards timing (compared to hose closed and timing advanced). So while it doesn't directly control timing, it does control the vacuum that does.

Thermistors could read in the hi 10 thousands ohm range.
Any chance you could get a part number off of them, you might be able to get the R/T characteristic curve from that, and see what the ambient resistance rating is - just as a check I mean?

I guess these things could fail open.
Don't know the 630 ckt so I don't know if jumping (shorting as a test) the temp lead to GND would hurt the relay. Thermistors would have some resistance, so if you shorted it, that line would see more current that it is used to. If the relay operated (with this test) of course that'd implicate the t'sistor.

no.
they have nothing to with timing.

the thermo time valve that DOES effect timing works off of heat from the engine only.

I have no idea why there are 2 temp sensors.

they are 95 and 60 degree sensors.
maybe Porsche wants to know when the engine is below 60 and above 95.
they look like open or closed switches, not really a temp sensor .

they have the same diagram symbol as the boost relay which is effectively just a switch.

I am going off this post by speedy squirrel in the distributer and timing thread.

http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/500986-ultimate-930-distributor-advance-retard-timing-turbo-lag-msd-mod-thread-27.html#post9103121

He describes how that switch engages the solenoid through the fuel enrichment control unit, which opens or closes the blue vacuum hose on the distributer, which does affect vacuum advance.

If this is not correct, what does the solenoid do? I just don't know.

thanks!

Does this help?

It looks like maybe the voltage changes as it heats up? I don't remember if I tested that...

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http://forums.pelicanparts.com/uploa...1490988955.jpg
http://forums.pelicanparts.com/uploa...1490988955.jpg

Assuming i did it correctly, the 93060611703 PN looks like it could be substituted with / sourced with a 'standard' part Ts-482, and their spec sheet indicates a snap-action /bi-metallic switch.
Switch is open until the set-point is reached.

Thanks!
So at temp, there should be continuity from the base to the lead, correct?
I'm not getting that on either switch. Open circuit regardless of temp.

that's my interpretation.
they're kaput

I hesitantly agree.

Jeff, double check MM. I know you know, just perform simple tests to make sure MM is functioning if you have not (which I am sure you have). Touch the leads, draw a heavy line with a carpenter's pencil to make sure it reads some resistance across a half inch.

Don't want you plunking money down if a MM anomaly.

Please post resolution.

I know the mm works.

I recently tested the resistance of the WUR successfully.
In fact, on one test Iof these switches, i started getting high resistance, but at least it read numbers other than open. Turns out I had my thumbs on both leads, but good advice regardless Bob.

A temperature switch is what the name suggests. A simple switch just like a relay. It's either on or off. A relay switches when you apply power to its coil and a temperature switch opens or closes when the switch temperature is exceeded. Internally there is a bi-metal contact that deforms with temperature change and when the switch closes it makes contact with the housing

A temperature sensor is a resistor that changes resistance with temperature. There NTC (negative temperature coefficient, more common) and PTC (positive temperature coefficient)versions available. Depending on the model they increases resistance with raising temperature or decreases resistance with raising temperature. The parts shown by the OP are switches though. They are normally closed. For the 15 degree C switch that means it will be open at room temperature. Put it into the freezer and then measure again.

Ingo

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Hi Jeff!

Did you solve your problem?

I have a similar problem on a 87 930.
The engine has been fully rebuilt, all sensors are new, i checked all the wires and everything is wired in correctly.

The soleniod valve vacuum line has been unplugged by the previous owner and i want to get everything working again, but i just can't get power to the soleniod from the Enrichment Control Unit, so there is no vacuum to the distributor retard as it should be.

The 35deg sensor has the part no. 930.606.117.03 and thats the same one that was in the car originally. But both the new and the old one are NC type sensors. Shouldn't they be NO like it is pictured in the wiring diagram?

maybe you can help me.

Thanks in advance and best regards from Germany,
Felix