Originally Posted by BobG

Update: With hot air now blowing independent of the temperature controls, I checked the duo valve once again and found that one of the solenoids had shorted out. Ugh.

I was tired of fiddling with the thing, so I ordered a new one from Autohaus for $148 plus tax with free shipping.



The DMM showed 21 ohms for each solenoid on the new duo valve, so I installed it yesterday.

I had been concerned about the difficulty of doing the replacement, especially those lower two hoses. As it turns out one does not touch the lower hoses. However, the two clips, one on each side of the duo valve, must be slid out. Slid out, not removed. See photos 1-3.

(Since I recently rebuilt the old duo valve with a new gasket and plungers, I am willing to pass them on to someone else for a reasonable price. Will also thrown in the original plungers which looked fine.)


Locking clip 1

Locking clip 2

Lower hoses exposed after duo valve removal

Old duo valve


The results of my web searches showed that Mercedes used duo valves in lots of their cars, but the assemblies differed and thus required different removal and installation procedures than for our Crossfires.

For an entertaining video showing a more problematic removal and installation, see "How to replace the Heater Solenoid Valve in a Mercedes SLK230" by Clint Hightower (https://www.youtube.com/watch?v=ioD1GOKyMB4). Clint comes off as a good guy, so I plan to watch his other videos.

I've also attached AR83.25-P-1150V "Removing, installing and replacing duo valve" for the later R171 SLK 320 which is close, but not exactly the same, as our Crossfires.