Thermo Time Switch – Bi-metal timing

[Peter]

Thermo Time Switch – Bi-metal timing

It is not clear for me how the Bi-metal timing of the thermo time switch is working.

1) Below 35 Degrees W is connected to de ground activating the CVS Solenoid.
2) When starting via the ignition switch G gets for +/- 2 seconds current, heating the heating coil
    around the bi-metal (for +/- 2 seconds)
3) Question: How can the Bi-metal, only with 2 seconds heating from G open depending the ambient
    temperature.

[Tyler S]

The lower the ambient/coolant temperature, the longer it takes the heating coil to bring the bi-metal strip up to the temperature in which it deforms and opens the circuit. The heating coil itself is not limited to 2 seconds of activation. It is energized and heating any time the key is in the start position and the internal contacts of the bi-metal strip are closed. Only to be cut off if either the key is released, coolant temp is above 35, or the heater itself has brought the bi-metal strip above the cutoff temperature.

[Peter]

From where the b-metal is getting its current?
G is only giving current during ignition period, +/- 2 seconds.
Is it W?

[Benz Dr.]

One other thing to consider: While staring your engine and it doesn't catch you will often find that waiting for a short while will allow the TTS to cool off and reset. If hitting your ignition right away doesn't seem to do anything this would be a likely reason.

I believe the G terminal gets a voltage signal while hitting the starter. W terminal is the one that goes to ground and quits working on a hot engine once the bi-metalic strip opens the contact points.

[Pawel66]

G is getting power when cranking only. Through the CSV relay, the steering circuit.

[Peter]

So this means the bi-metal gets current via W as long as it is closed.
When it opens the current stops to heat-up the bi-metal and the CVS solenoid is closed.

This is logic, but why does it need G for only say 2 seconds during the ignition/cranking.

[Benz Dr.]

So this means the bi-metal gets current via W as long as it is closed.
When it opens the current stops to heat-up the bi-metal and the CVS solenoid is closed.

This is logic, but why does it need G for only say 2 seconds during the ignition/cranking.

G will go to open when the thermo strip heats up determined by how cold the engine is ( longer duration when really cold out ). W will then have no ground and will also become open until G cools off.
 Once the engine is heated up the thermo strip on G will open and nothing will go to ground until the engine cools off. It's not complicated but there's more than one thing going on with a cold engine. Plus, I've never been good with electronics and could be wrong.

Tyler, mark my test papers please.

[Pawel66]

Starter solenoid is connected to connector 86 on CSV relay (steering) and this is connected to G. Connector 85 of this steering is connected to W and to ground when cold.

You turn the key. Starter solenoid gets power so relay gets power and G gets power. Through W it grounds the circuit for relay to give power to CSV. CSV injects gas. But when G gets power, bi-metal heats up and after some time (depending on coolant temperature and specified on TTS housing) disconnects W. No ground to CSV relay, no gas injected any more.

This time when CSV is activated, depending on TTS type, condition and coolant temperature is a major headache and may be an issue with cold and warm start, as TTS and CSV should work during the warm start too. And you need to be mindful of Benz Dr. (modified, sorry) is describing to survive.

I switched to modern Bosch TTS.

[Tyler S]

A+ Dan and Pawel

Peter, there is no set +\- 2 seconds within the TTS. Only on systems that were adapted with a 1 second CSV activation timer switch was the TTS ignored and gave the engine a 1 second shot of fuel during any and all operating temperatures.

[Peter]

Very clear Gents I was only looking to the TTS.
I will put it in a diagram, the TTS and relay.

Pawel, which modern Bosch TTS (type number) are you using now?

[Pawel66]

It has been about a million posts ago, but I found this picture note attached. I will provide link to post if I find it..

[Pawel66]

Yes, this one obviously:

https://www.sl113.org/forums/index.php?topic=24565.msg175598#msg175598

and this is with details:
https://www.sl113.org/forums/index.php?topic=26041.msg186571#msg186571

[Peter]

Thanks.

[Peter]

It is now clear.
My mistake was that I thought the time cycle would always be completed, but this is not needed when the engine starts earlier.   

The thermal switch works as long as you start, with a maximum of the specified seconds and temperature as specified during and until you stop starting. If the engine starts earlier, the entire process stops earlier because the engine is running.

If you continue starting, the process will stop after the specified period and prevents the engine from drowning.

[ja17]

Correct Peter, also remember the TTS does not directly activate any starting aids, the TTS activates the relays which activate the starting aids.

[Benz Dr.]

This why it's a good idea to remove fuse number 4 ( to the electric fuel pump ) when doing compression testing or turning your engine over with your starter.