How does washer pump work ?

[J-N995]

So I've a few issues but working through them slowly.

One is washer pump. Motor is fine as I've bench tested it.

I've got 12v on the two pump wires. But when I press the stalk nothing happens.

How does the switch actually work ? If there is constantly 12v to it. .

 

[stwat]

What car? The washers should only work when the headlights are on.

 

[DSM10000]

What car? The washers should only work when the headlights are on.

Not windscreen washers

Other posts by the O/P mention a W204 that was bought with faulty wipers and washers.

Has the washer stalk been checked?

 

[whitenemesis]

Doors closed and bonnet properly shut?

 

[brucemillar]

Push button really hard.

Sent from my iPhone using sausage fingers.

 

[J-N995]

Sorry guys.

It's on a 2008 c320.

I have tried pushing the stalk hard..with no joy.

I'm just confused to why I have power on the cable but no motor spinning.

 

[PobodY]

If you've got power at the plug, and the motor turns on the bench; a dodgy connection?

 

[Larkone]

If you've got power at the plug, and the motor turns on the bench; a dodgy connection?

Or the pump is failing to spin up once under load in the car and trying to pump water.

 

[Codger49]

Might it have a switched earth rather than a switched live?

 

[brucemillar]

^ This.

 

[garycat]

Have you checked for a blockage in the pipes? The non-return valves can become suck and stop water from squirting out (but you do normally get a bit of a dribble)

 

[PobodY]

Might it have a switched earth rather than a switched live?

Is it one of those motors that spins one way for the windscreen and the other for lights (or the rear window)?

 

[Codger49]

After a few years, it has been known for washer reservoirs to accumulate a layer of 'gunge' which could well block the pump's input. Might be worth checking for this.

Think it arises from mixing different types of screen wash additive.

 

[J-N995]

So I've had it diagnosed as the front sam unit.

The garage checked the stalk on the star computer and it was working.

I have found a front sam unit with the exact same part number for less than half the price of mercedes.

Does anyone know if I could do a straight swap as it is the same part number and off same car.

 

[whitenemesis]

Might need coding to match exactly the options fitted to your car..

 

[J-N995]

Might need coding to match exactly the options fitted to your car..

Thank you

Got it booked in with prestige all parts on Friday

They sound they know what there doing.

Took it to a garage who said he has star diagnostic. Turned out it was snap on scanner :/ no wonder they couldn't code them