JimmyKudo

Hello All,

The heat comes on in my W204 only for the first few minutes of driving. It comes on if I keep the RPM above 5k or so as well, albeit weakly.

Info:
- Blower works fine on auto/manual AC modes. If I tell it to go full blast it stays there indefinitely.
- Heater failure is on manual and auto modes
- Floor vent, defrost, and regular vents all switch flawlessly
- Heat works only for the first couple minutes (I believe this is electrical heat before the coolant is supposed to heat up the heater core)
- High RPM heats up the car which leads me to suspect it involving coolant flow

I believe the heater control valve (A 271 203 01 64) is the culprit. I thought it might be the blower resistor/regulator (aka the hedgehog) since it had "fins" that looked like they were for heating, but it doesn't share failure symptoms. In-car temperature sensor is also probable, but when the heat comes on it stays on at high RPM and for the first few minutes, so I don't think that's related.

Please help!

Edit: I should note that I believe that part number is the closest number I could find to the "heater control valve"; I found a good guide on how to change this for the V6 C350 but not the C250. The part number could just be for the coolant flow to allow the engine to warm up, though the fact that this valve actuates after warm up (and since my heater fails after warm up) leads me to believe it's related to the failure in some way.

xsever

I would get the car scanned for codes before starting to throw parts at it as that could turn out expensive.
To get the right part number though for your car, go to mboemparts.com and browse there.

JimmyKudo

I haven't yet purchased any parts, so costs in this are just my own research time. Thanks for the recommendation; I'll consider it if my research isn't conclusive.

JimmyKudo

Bumping.

JimmyKudo

Still haven't been able to figure it out guys. Can someone point me to a diagram of the heater system on the W204 C250? Since my symptoms are very peculiar I feel like I might be able to narrow it down with a high degree of certainty.

If not, I'll go forth getting it scanned if it's cost-effective like xserver mentioned or replace some possible culprits if that's much much cheaper than the scan. I'll post the findings and results!

To that effect if anyone knows where a guide or just the location of the heater control valve is on the I-4 version of the car (there's a nice guide on the V6 version, but not this one), please send me a link.

Eric1983

I had a similar issue with my C180 CGI. Agents initially fobbed me off. Pulled in there the one day in the middle of winter and the service advisor couldn't believe that the aircon was blowing a gale. They had the car for about a week before coming back to me. They said that the heater has an auxiliary water pump which had failed. Perhaps you have a similar problem?

JimmyKudo