OK, this is starting to get annoying. Once the temps drop below 30F, the passenger side headlamp washer quits spraying. It will still deploy, just no spray.
I have been to the dealer twice, on the second time they replaced the unit. That fix only worked until the temps dropped again.
This only happens with the passenger side. I have purged the system and refilled several times with washer fluid rated to -30F, and no change.
As I said, only the passenger side does this. Every other washer works fine. Drivers side, rear, front windshield are perfect even when it was +1 this morning.
Any ideas???
Is there some chemical additive I could use that would help??

I have also thought of going under the front bumper and figuring out some way to insulate the washer tube that feeds that washer, but it's a little too cold to play mechanic now.

 

It's been -30 here for several days now and using similar windshield washer fluid I have had no problems. It has to be a plumbing problem with perhaps a pinched line that gets worse in cold temps. Make the dealer keep searching.

 

In extreme cold , less than 10 F mine freeze up and do not extend, or I should say one of them at random. The ones in my 02 did the same thing but at temps above that they work just fine. Could be routing of the tube that goes to the washer in your case.

 

As an update, I tried a purple brand fluid that was rated at -35, and today with temps in the 20s they worked OK. Will continue to monitor with this fluid.
Looks like it is a combination of washer fluid and degreaser.

Over the next week temps should drop to the -'s so that will be a real test.

 

The "Purple Power" brand that I tried is a success!! Today with temps around -6F, and the car sitting outside overnight, first thing this morning they both sprayed, and continue to spray on demand all day!!
The product is rated to -35, so the extra methanol could be the cure. Or maybe they actually put some R/D effort into their formula.

As a side note, I did notice that Mercedes website shows that the headlamp washers for 2009 are now heated! Wonder if I could retrofit??