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My heat in the cabin of my W211 E320 CDI cut out a few week's back (blowing cold all the time, unresponsive to controller on high temps, same at the front and rear seats). Engine water temp on the main gauge showing temps like normal, no issues there.
I initially diagnosed what I thought was an Aux water pump in the system below the windshield wiper cowl (connects right into the heater core just on the engine side of the firewall). I replaced this part (part #A211 832 0084 - see photo), but once I had it on the bench, I realized it wasn't a pump at all, but a control valve! Duhh. I must have been rushing and not thining when I made the diagnosis.
Bench testing the old and new, I realized it valve opens with 12V one polarity, closes when polarity is switched. Old one was working fine, but replaced it while I was in there.
The curious part is, that while I was waiting for the new part to arrive, I had the old one unplugged from the 12V connector for a few weeks. During this time, heat was immediately working again as normal!
So now I'm scratching my head as to what could hav ebeen causing it to close incorrectly, some sensor perhaps? Or some other diagnosis unrelated to this, but with the heat working again when it was unplugged, I'm quite confused.
I haven't had a chance to test the new one I installed yet and see if the heat is shutting off again now that everything is installed...
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Slideshow: A one-of-one U.S.-spec Mercedes-Benz SLR McLaren Roadster became even rarer after a factory-backed transformation at McLaren's headquarters.
