Testing the Thermo time switch

[Vereeken]

I have tested the thermo time switch by measuring what voltage I get on the CSV.

I am confused by the results. Can anyone straighten me out?

With the multimeter probes connected to the connection I have pulled from the CSV i get the following:

1. with connections to the TTS both off. I get 0 at CSV when starting. I believe that is correct as I have interrupted the Ground to the CVS.

2. with both connections to tehe TTS connected. I get 9v at the CSV when starting. I am guessing this is actually 12 V but the MM is not fast enough to measure because teh car starts right away and I let go of the starter.

Now for the strange part. When I swap my TTS connections I also get 9v at the CSV.

Where is my error in thinking?

This is on a 911 SC ROW model.

Michel

[T77911S]

why are you messing with it if the car starts right away?

it depends on how you measure it. (this is why i think a test light is better, especially for those that dont really understand electronics) (if a test light is used, you either measure from ground to 12v or 12v to ground...for the most part.)

if you are measuring power at the CSV connector, from pin to pin, and the wires are removed form the TTS, you will get 0v. that tells you nothing. you should either measure (from pin to pin) with the ground connected at the TTS, to test the entire circuit, or measure from (CSV +V pin) to ground to test for 12v to the CSV.

another way to test it is to remove both wires from the TTS and test each one to ground. then with the TTS cold, you could measure resistance of each terminal to ground. i dont know what the heater side should be but the CSV side should be close to 0 ohms.

pull off the connector to the CDI and the FP relay to start it longer. you can also remove the heater side to the CSV if you need it to stay closed longer.

[Vereeken]

I am testing it so I get the wires at the TTS OK.

I have a VDO TTS and not a Bosch. As a result I have no G and W marking.
So I tried to establish which is which by measuring Ohms.

At dead cold i have 0,7OHM on one , that tells me that one is W-.
The other gives me 24,2OHM so that should be G+

I measured these ohms from terminal to TTS body. They should be within spec.

So if I know G then that tells me that the Yellow wire should go to G and the brownish/red wire should go to W.

Thinking further if all is connected well at the TTS I should see 12V at the CSV terminal on a dead cold engine when cranking. And I see that (I even see the full 12 V if I crank for a second or 2/3).

So going further I assumed that when I would swap the wires over I would see again 0V at the CSV As I have "broken" the ground to the CSV.

But strangely enough it gives me again 12V.

So I am guessing againn but what I think I did was simply give the CSV another path to ground., and with the wires swapped I think i would see 12v all the time at CSV. So installing the wires incorrectly would give you CSV action all the time and would eliminate the heating element of the TTS. Installing them correctly would give you CSV with TTS heated so a max of 8 seconds of CSV action when cranking.

But I might be missing something.

Michel

[T77911S]

this goes back to what i said at first. not to be insulting at all, but here is where electronic/electrical theory comes into play.

remember this, you have to have resistance to measure voltage.
if the ground side of the CSV is grounded, then you will read 0v because the switch (basically) has no resistance (.7 ohms). but on the other hand, if you remove the wire from ground, you will read the full 12v because now you have infinite resistance.
or, look at it this way. the grounded side of ANYTHING is electrically the same point as ground and ground to ground = 0V.

here is another test.
connect a light bulb across a battery. if you measure the hot and the ground side of the bulb, you get +V. if you measure the ground side of the bulb to the NEG on the battery, you get 0V, but remove the wire from the NEG on the battery and measure V from the wire to the battery, you get +V.
now siwtch to amps and you can measure amps this way. V/I (amps)= bulb resistance. measure bulb resistance, should be the same.

now, with a cold TTS, you should see 0v at W while cranking UNTIL the switch opens, then you should get the full 12v. (i have not tried this, just electronic theory).

if you connect the CSV (ground) to G, it should stay on all the time. 24 ohms (heater) is not enough resistance to keep the CSV from working.

measure your voltages to ground to check for power or V. you can then measure from +pin to -pin to make sure the wire going to ground is good.

but, it sounds like you have the wiring figured out.


it was not a good day for me when my brother bought a multimeter....lots of time on the phone.