A150 W169 wash problem

[Stuoyb]

Hi, hope there is someone out there that might be able to help.
Got a puzzling issue on the front/rear wash.
Have checked the system and the pump is OK, however intermittently the front screenwash does not work but the rear one does instead.
As there are only two wires connected to the pump there is obviously a relay to switch pump direction between front/rear wash - but where is the relay?
Can't find any reference to a relay in the main fuse box - does anyone know where or what it is?

 

[mattkh]

On your year car, can you just turn the rear wash/wipe? If yes, what do you press to action that.

 

[Stuoyb]

The control stalk has three sections, one for the front wipe (intermittent/slow/fast), a second control for the rear wipe/wash and a button at the end of the stalk for the front wash/wipe function.
The front wash sometimes works but sporadically doesn't but the rear wash operates instead leading me to suspect a faulty relay which I cannot trace.

 

[mattkh]

Why are you ruling out a faulty stalk ??

 

[Stuoyb]

Good question.
As there are only two wires on the pump and two outlets, I was guessing that a relay was used to switch rotation of the pumps to feed either front or rear.

 

[umblecumbuz]

... or even a partially-blocked front set, throwing a fail safe function that prioritises the rear washer.
Guessing in the dark here, but any port in a storm (apologies for mentioning lots of water).

 

[mattkh]

Ignore my comment about ruling out the stalk.
I have just been able to refresh my memory. The mechanism to divert the water is inside the 'pump'.
The motor in the pump goes one way to send the water to the front pipe. When the motor in the pump is made to turn in the opposite direction, by switching the polarity, the water goes to the rear pipe.
Inside the socalled 'pump' is a rubber bung that moves right or left.
Last time I worked on these hoses, they were difficult to remove. However I know that it is easy to pull up the 'pump' with the hoses attached. Dont know about the length of the cable. If you want to do that, be aware of a rubber O-ring at the bottom. You should be able to reuse it.
O.K. with the mechanism up, rock it a few times and/or warm it up a bit, and push it back in and test.