Windshield washer fluid pump testing. - PeachParts Mercedes-Benz Forum

azitizz · #1 02-14-2011, 10:23 PM

I think I have two botched washer fluid pumps, but wondered if anyone with a bit more electrical knowledge could add their two cents.

On my 85-300TD wagon, the front windsheild pump seems to have stopped working.

I had to re-wire it last year to make room for an Espar diesel pre-heater and put the fluid resevoir on the passenger side of the engine. I checked the wiring with a meter and when I press the washer fluid button (on the turn signal) it still gives me a reading if just over 12 volts when the button is pressed and the probes in the socket for the pump wiring.

I figured this must be a pretty good indication. I thought i could just take the rear window pump as they are the same but it also wasnt working, but has been disconnected since we bought the car 3 years ago.

Using a continuity setting on the meter I put the probes on the two prongs of the pump and one of them gave positive continuity and the other pump was a negative.

I was wondering if I simply put two wires connected to a 12V battery and connected them directly to the prongs of the pump, would it normally activate the pump? Or would it fry it?

Any other suggestions no how to make a test to see if they are indeed both broken before buying a pair of new ones?

dieseldan44 · #2 02-14-2011, 10:59 PM

Quote:

Originally Posted by azitizz

I think I have two botched washer fluid pumps, but wondered if anyone with a bit more electrical knowledge could add their two cents.

On my 85-300TD wagon, the front windsheild pump seems to have stopped working.

I had to re-wire it last year to make room for an Espar diesel pre-heater and put the fluid resevoir on the passenger side of the engine. I checked the wiring with a meter and when I press the washer fluid button (on the turn signal) it still gives me a reading if just over 12 volts when the button is pressed and the probes in the socket for the pump wiring.

I figured this must be a pretty good indication. I thought i could just take the rear window pump as they are the same but it also wasnt working, but has been disconnected since we bought the car 3 years ago.

Using a continuity setting on the meter I put the probes on the two prongs of the pump and one of them gave positive continuity and the other pump was a negative.

I was wondering if I simply put two wires connected to a 12V battery and connected them directly to the prongs of the pump, would it normally activate the pump? Or would it fry it?

Any other suggestions no how to make a test to see if they are indeed both broken before buying a pair of new ones?

Almost always, DC motors in pumps fail 'open'. Using an ohm meter, measuring between the two terminals a DC motor should read a low value, well under 100 ohms. If it is higher, it is usually bad. If it is open (infinity ohms, or the same as not touching the probes to anything) it is definitely bad.

You can hook them up to a 12V DC power source for testing. If you hook it up backwards, it spin the wrong direction - not a big deal. Try to observe the proper polarity and you will be fine.

You can also hook them up to a lower voltage source, say a 6V lantern battery. They will spin half speed, but it's not as dangerous as messing around with a car battery to test a little motor.

azitizz · #3 02-14-2011, 11:00 PM

I see I can buy a pump for either $20 for OEM or $12 for an MTC. Im eyeing the MTC, can they be so different in quality?