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Thermo time switch testing
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Mr Brown
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PostPosted: Sat Mar 06, 2010 10:36 am    Post subject: Thermo time switch testing Reply with quote

I am troubleshooting a warm start issue and would like to know if anyone has bench tested a thermo time switch. The engine is partially disassembled right now so I can't test per the Bentley. The L-Jet manual says that the switch should be open at 104 deg F. All I get is approx 135 ohms on the four different switches I have when they are heated above 104. It is possible that I have four malfunctioning switches, they are all used. Any one know if this is normal?
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Randy in Maine
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PostPosted: Sat Mar 06, 2010 2:34 pm    Post subject: Reply with quote

Did the residual fuel pressure test rule out a fuel delivery problem? That would be far more likely to be the problem.

http://www.itinerant-air-cooled.com/viewtopic.php?t=213
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tencentlife
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PostPosted: Sat Mar 06, 2010 7:34 pm    Post subject: Reply with quote

It's easy to test on the bench. You need a 12V battery. The pins are lettered W and G. G is the heater circuit, W is the switching circuit, and the body of the switch is ground. With the switch at room temp, ohmtest both pins to ground. G should have some resistance, W will be near zero ohms. Now ground the switch body to your 12V battery and power G while ohmchecking the switching circuit W. After about 8-10 seconds of heating, the switch should open. It should close again if you cool the switch.

If the heater circuit is broken, the TTS can still be useful if the switch itself responds to temp and opens. You can test this by warming the switch in hot water or a very gentle flame. I think the opening temp is 30 or 35C, typically.

If you ever suspect the TTS is causing a warm-starting problem on a CIS car, you just unplug it. If the TTS has failed to ground, the TTS will be grounding the CSV circuit when cranking, so it floods. Unplug the TTS, you unpower the CSV so no flooding.
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Jeremy81
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PostPosted: Wed May 18, 2011 1:53 pm    Post subject: Reply with quote

According to the Bentley to test the thermo time switch TTS you unplug the cold start valve CSV, disconnect the green ignition wire from the coil, place a test lamp across the CSV connector, and have an assitant crank the engine over. If the TTS is working, the test lamp will "flicker" for approximately 12 seconds (depending on the current temperature of the engine). I realize this thread was focusing more on bench testing, however, I have a few questions regarding the Bentley test method.

First, performing the above procedure, what should the measured voltage across the CSV? I prefer voltage rather than watching a test lamp flicker. I recently ran the above test with a multi-meter and measured +- 5.5 volts. According to the manual the voltage should drop after 12 seconds or so, due to an internal heating element. This is assuming of course I know what the starting voltage should be to begin with, which brings me to my second question.

Second, what voltage is necessary to open the CSV. Another way to ask the question, what is the voltage signal from the TTS?
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tencentlife
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PostPosted: Wed May 18, 2011 7:09 pm    Post subject: Reply with quote

If you study the wiring diagram for a bit this all becomes clear. One CSV pin gets voltage right off the starter #50 (solenoid trigger) circuit. Therefore the voltage across the CSV pins is the solenoid trigger voltage, which should be battery V but V is depressed by the starter load when cranking, so it will test quite a bit lower than 12V.

The TTS just grounds the other CSV pin, so there is no "signal", just a connection to ground which opens after the specified time period of cranking (the "time" function) or which opens when the TTS temp is above the setpoint (the "thermo" function). The time function is actually attained by the cranking current warming the thermo-element in the TTS until it causes the grounded pin to open, so even the time function is really just a thermal function.

I swear, this is so much simpler when you look at the skiz than trying to describe it.
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Jeremy81
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PostPosted: Thu May 19, 2011 12:54 pm    Post subject: Reply with quote

Thanks Tencentlife your explanation is quite clear. I should have looked at the diagram first. Knowing this, here is how I will run the next test. With the engine completely cold I will disconnect the CSV, run a jumper wire to the positive side of the coil and another jumper wire to ground. This way I can operate the CSV at will. Then I will operate the fuel pump (via the MAF shut off) to "prime" the fuel system. Before starting the engine I will run the CSV for a few seconds to spray fuel into the air plenum. With the CSV disconnected and my multi-meter ready I will ask the help of a very lovely assistant to start the engine. If the TTS is working the voltage at the CSV connector should drop to zero after warm up, right? This would indicate and open circuit. If it remains closed, then I can assume one of two things. One, the TTS is faulty or two, the wiring from the starter to the TTS is faulty. Furthermore, we should be able to eliminate the wiring to the CSV, simply because we have voltage at the CSV connector, no? This is fun, and I can't wait to get the lovely assistant to lend a hand here. Let me know if think I left something out?

Thanks for all your help!
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tencentlife
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PostPosted: Thu May 19, 2011 4:00 pm    Post subject: Reply with quote

Quote:
Let me know if think I left something out?


Flowers for the lovely assistant? Maybe a nice chocolate sampler?

I'm not exactly following your testing plan. I think you may still have one of the most (probably the most) common misperceptions about the CSV/TTS system, which is that it has a role in warmup. It does not. The power supply for the CSV is, as I said, direct from the starter solenoid trigger circuit (#50); stop cranking the starter and the power to the CSV stops as well. It only has a role when actually operating the starter, once you relax the key the CSV is offline no matter what the condition of the TTS. So:
Quote:
If the TTS is working the voltage at the CSV connector should drop to zero after warm up, right?


Voltage across the CSV connector would drop to zero when your comely compatriot stops operating the starter regardless of the TTS condition.

The TTS provides the logic for operating the CSV while cranking by grounding or not grounding the other side of the CSV injector coil. When cool, the thermal contact inside the TTS is closed and thereby grounds the CSV (via the TTS body casing). When warm (above the spec printed on the TTS body, usually 30 or 35C as I recall) the thermal contact opens passively. The thermal contact is a bimetallic spring so it bends a certain amount when warmed to a certain temp, the tip of the spring carries the contact so by bending, it mechanically opens the CSV grounding circuit. The time function is provided by circuit #50 actively applying heat to the bimetallic spring thru a heater wire wound around the spring; crank for several seconds, and the spring warms, bends, opens the contact and the CSV stops spraying, to avoid flooding the engine even when the engine is cold.

Wait a minute or two, and with a cold engine the thermal contact will close again, and you can attempt to start the engine once more. That also means that cranking for more than the specified 8 or 10 or 12 seconds is pointless because the CSV will have stopped spraying.

That's it, it's called the thermo-time switch because it provides both a passive temperature-dependent grounding for the CSV, and a time-dependent function based on the amount of time the starter is operated.

And if you already understood all that, then excuse me because I didn't get that from what you wrote.

I can't think of a simpler and more direct way of checking the TTS than what I described above, which you can just as easily carry out with it installed, with a testlight or ohmmeter, and a jumper wire. The TTS is already grounded so you can borrow power off the alternator pole to apply power to the heater circuit (pin G). The testlight can be connected to the alternator power there and grounded at pin W; it should go out after the specified time interval:
Quote:
It's easy to test on the bench. You need a 12V battery. The pins are lettered W and G. G is the heater circuit, W is the switching circuit, and the body of the switch is ground. With the switch at room temp, ohmtest both pins to ground. G should have some resistance, W will be near zero ohms. Now ground the switch body to your 12V battery and power G while ohmchecking the switching circuit W. After about 8-10 seconds of heating, the switch should open. It should close again if you cool the switch.


Although maybe you have an ulterior motive, which is not to prove anything conclusively so the winsome wahine will have to stick around and help until, say, it's time for dinner? You sly devil, you.
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Jeremy81
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PostPosted: Mon May 23, 2011 12:23 pm    Post subject: Reply with quote

Thank you Tencentlife for your detailed responses. I've tracked down the cold-start gremlin. While replacing all of the fuel injector connectors, including the TTS and CSV, I carelessly switched the G and W wires. Therefore, as you pointed out the switch was not able to properly ground the CSV under cold start operation. This explains why I was reading a constant 5.5V under all operating conditions.

In hindsight, my testing plan was somewhat contrived. Had I spent a little more time studying the wring diagram, and becoming more familiar with how the cold-start system operates, I could have avoided this question.[/quote]
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vw66bus
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PostPosted: Mon Jan 08, 2024 3:52 pm    Post subject: Re: Thermo time switch testing Reply with quote

Happy New Year 2024.
Reviving an old thread.

My situation:
81 aircooled vanagon.
hard to start cold, (or cool here in TX, let's say 1st start of the day, subsequent starts are relatively quick if not immediately.)

When I used a test light from chassis gnd to + on Cold Start Valve (herein CSV) connector +wire I see no flicker or any light on the test light during crank/start. (Yes, test light was verified good)

Measuring resistance on both pins of the CSV connector gave ~0 ohms during key-off. I probably used to high of a scale on my non-auto-ranging multimeter. Engine was cold (<70 deg F).

I replaced the CSV w/ one from a 280Z or 260Z (autozone #800-2032, had to replumb the fuel line for single input vs. pass thru). CSV clicks when i power/gnd it externally.

Where do I start looking/probing on all of the white wires (thanks VW!) for the Fuel Injection.

peace,
marc
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Wildthings
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PostPosted: Mon Jan 08, 2024 5:54 pm    Post subject: Re: Thermo time switch testing Reply with quote

The cold start valve gets it power from either the #50 or the unlabeled spade on the starter solenoid. On a Bay the power first goes to the Double Relay where it is shunted to the CSV so I would assume its the same on a Vanagon. You need to figure out and test this circuit. The circuit is only energized during cranking, but you could momentarily apply power to it at the solenoid end and see it that caused the CSV to spray. The engine needs to be cold for the TTS to activate the CSV, if the engine is warmer than around 100-120°F the TTS isn't going to allow the CSV to spray.
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