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Only 10.6V at sink water pump. How to diagnose? *SOLVED*
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sphet
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PostPosted: Sat Jul 11, 2020 6:07 pm    Post subject: Only 10.6V at sink water pump. How to diagnose? *SOLVED* Reply with quote

My water pump failed over the winter, likely from freezing water inside it. While hooking up the new one I noticed I am only getting 10.6V power. My battery is at 12.6, as is the voltage at the fuse under my driver’s seat when I test it against the chassis. The sink reads 10.6 regardless of whether I test power against the chassis or back through the wires that are part of the two-terminal connector.

Now that I think of it, my battery level display on the front of the kitchen only ever shoes green when I have just turned off the engine, so likely it is getting low voltage too.

Any ideas to try without pulling my kitchen?

Can I pull the control board out without pulling the kitchen so I can measure voltages on the backside?

S
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Last edited by sphet on Tue Jul 14, 2020 6:01 pm; edited 3 times in total
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fxr
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PostPosted: Sat Jul 11, 2020 6:16 pm    Post subject: Re: Only 10.6V at sink water pump. How to diagnose? Reply with quote

Probably dirty contacts in the connectors that join it all up. You did check the o/p of the fuse not the i/p? That fuseholder <spit> is notorious for bad connections, not only to the fuse itself but also the screw terminals.
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sphet
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PostPosted: Sat Jul 11, 2020 6:21 pm    Post subject: Re: Only 10.6V at sink water pump. How to diagnose? Reply with quote

fxr wrote:
Probably dirty contacts in the connectors that join it all up. You did check the o/p of the fuse not the i/p? That fuseholder <spit> is notorious for bad connections, not only to the fuse itself but also the screw terminals.


I do not have the pillar-mounted fuse, only the one under the driver’s seat. I replaced it with a marine grade inline fuse with the rubber cover. There’s no easy way to measure the output side. I guess I could jump the fuse and measure the voltage again. Could a bad fuse cause a voltage drop? Thanks for the suggestion.

I get 12.6 testing either side of the blade fuse against the chassis, using the exposed metal on the back side of the fuse.
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PostPosted: Sat Jul 11, 2020 9:37 pm    Post subject: Re: Only 10.6V at sink water pump. How to diagnose? Reply with quote

A bad connection can cause the voltage drop. Use your dvom and check the positive side with one lead on the positive wire at the pump, the other lead at some other end of the positive cable. Operate the pump and see what the voltage is. Typically you don't want to see more than 200-300mV on the positive side and no more than 100mV on the negative side. You can move the probes around to pinpoint the voltage drop.
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crazyvwvanman
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PostPosted: Sun Jul 12, 2020 5:23 am    Post subject: Re: Only 10.6V at sink water pump. How to diagnose? Reply with quote

You have an early Westy and on many of those the led panel has a big transistor that controls power to the water pump.
This was done to disable the pump when the water tank sensor circuit thinks the tank is empty.
This protection feature complicates the diagnosis since there is no direct connection between the battery voltage and the voltage seen by the pump.

Look at your led panel, left side set of leds for the water level.
If you have 2 reds on the left bottom then the panel is one with the pump protection transistor.



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Mark
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sphet
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PostPosted: Sun Jul 12, 2020 7:24 am    Post subject: Re: Only 10.6V at sink water pump. How to diagnose? Reply with quote

crazyvwvanman wrote:
You have an early Westy and on many of those the led panel has a big transistor that controls power to the water pump...Look at your led panel, left side set of leds for the water level.
If you have 2 reds on the left bottom then the panel is one with the pump protection transistor.
Mark


Mark,

That’s what I have. I was doing my test with water in the tank but I did not consider the impact on voltage via the water level circuit.

A question - you have your panel illuminated but removed from the kitchen. Can I at least pull the harness forward to check voltages on the harness without pulling the kitchen unit as a whole?
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PostPosted: Sun Jul 12, 2020 7:40 am    Post subject: Re: Only 10.6V at sink water pump. How to diagnose? Reply with quote

crazyvwvanman wrote:
You have an early Westy and on many of those the led panel has a big transistor that controls power to the water pump.
Mark

Wow, you never cease to amaze me with the depth of your knowledge of these vehicles!

Thank you so much for contributing your valuable time and expertise here.
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crazyvwvanman
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PostPosted: Sun Jul 12, 2020 7:52 am    Post subject: Re: Only 10.6V at sink water pump. How to diagnose? Reply with quote

Yes, you can pull it forward. The wiring behind the panel might prevent you from pulling it out much, depending on how someone routed the wires. There is a large connector that can get caught between the sink bowl and the stove board so be careful.

That isn't my photo, just one from the Samba Gallery.

Mark

sphet wrote:

A question - you have your panel illuminated but removed from the kitchen. Can I at least pull the harness forward to check voltages on the harness without pulling the kitchen unit as a whole?
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sphet
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PostPosted: Sun Jul 12, 2020 4:54 pm    Post subject: Re: Only 10.6V at sink water pump. How to diagnose? Reply with quote

I tested for 12V at the multi-terminal connector (both sides) and then at the base of the switch on the surface of the panel where the orange wire brings power to the panel. I got 12.7V. When I tested the outbound voltage on green which leads to the water shutoff sensor it is 10.6V so my testing can only lead me to believe the voltage drop is coming from something in the panel. My high school electronics classes are of the same vintage as this bus, so I’m stuck at this point.

Any ideas? I suppose I could bypass the panel completely but I don’t want to butcher my system.

I see that Go Westy sells a replacement panel but I am assuming it is for the later buses. I don’t have the blue pilot light sensor on my current panel. Is there an option for earlier buses?

Thanks everyone for the help so far. I’m going to go and hookup the new pump even if it is only running 10.4V.
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PostPosted: Sun Jul 12, 2020 5:13 pm    Post subject: Re: Only 10.6V at sink water pump. How to diagnose? Reply with quote

In mid 82 and later vans VW dropped the transistor control of the pump and that is what you could do also.

There is a power wire into the panel and another wire that takes the power to the pump/faucet switch. Connect the pump/faucet switch wire to the panel power wire, like VW did in later panels.

Mark



sphet wrote:
I tested for 12V at the multi-terminal connector (both sides) and then at the base of the switch on the surface of the panel where the orange wire brings power to the panel. I got 12.7V. When I tested the outbound voltage on green which leads to the water shutoff sensor it is 10.6V so my testing can only lead me to believe the voltage drop is coming from something in the panel. My high school electronics classes are of the same vintage as this bus, so I’m stuck at this point.

Any ideas? I suppose I could bypass the panel completely but I don’t want to butcher my system.

I see that Go Westy sells a replacement panel but I am assuming it is for the later buses. I don’t have the blue pilot light sensor on my current panel. Is there an option for earlier buses?

Thanks everyone for the help so far. I’m going to go and hookup the new pump even if it is only running 10.4V.
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PostPosted: Tue Jul 14, 2020 4:31 pm    Post subject: Re: Only 10.6V at sink water pump. How to diagnose? Reply with quote

Mark,

You are suggesting I take the control panel out and remove and resolder the power out to the switch so it isn’t affected by the transistor? The only thing I lose is the low-level shutoff?

So remove yellow (switch according to bentley and makes sense it is on the transistor) from the transistor and solder it on other side of switch from orange (+)?

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I also finally found this link: https://www.thesamba.com/vw/forum/viewtopic.php?t=395922&start=0

Where you generously give the information I asked again. Thanks for your help and time.

I think this is my move as my pump doesn’t have enough juice at 10.6 to prime let alone maintain any velocity. I am wondering - could a frozen pump blow the transistor? All this seems to have happened at the same time.
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PostPosted: Tue Jul 14, 2020 5:59 pm    Post subject: Re: Only 10.6V at sink water pump. How to diagnose? Reply with quote

So I followed Mark’s advice and moved the yellow wire to the trace on the other side of the power switch. Now I get correct house battery voltage of 12.6V. The only thing I lost was the low level cutoff.

Thanks so much Mark.

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