PeachParts Mercedes-Benz Forum - View Single Post - 300E

hispassion · #21 08-27-2007, 05:05 PM

Wow, thanks guys for all the input. This along with gnashing my teeth has helped eliminate a few things. These are the things I know it's not.

1) It's not a voltage issue.
2) It's not the compressor clutch or Klima (MAS) relay.
3) It's not (at least for now) the vacuum pods.
4) It's not a refrigeration issue (suction line cold during heat up)

This morning on the way to work, I had a rather warm ride in. The ambient was 89°F and without many rpm's at all, I had temps up over 100°F and at one point (during heavy acceleration) it got to 110°F. Since it was only 89°F outside, 110°F at the vents had to be heated air.

When I got to my favorite (no shade) parking space at work, I opened the hood and felt the suyction line. It was cold and sweating. The heater hose (on the same side of the car [outlet?]) was hot as was the aluminum futher in towards the heater core.

So, at lunch I grabbed my pinch-off pliers, asked the fleet tech here if I could borrow another pair and I pinched off both the inlet and the outlet to the heater core. Then I went for about an 8 mile drive. The ambient was 102°F. The vent temps were 60°F regardless of rpm, fan function, vehicle speed or acceleration.

Therefore, it has to be hot water (coolant) getting into the heater core. Now, before I told you all that I pinched off the inlet to the heater core and this is true. I also pinched off the outlet to the heater core with no change in symptoms. But when I closed off both inlet and outlet, there is plenty of cool air.

And I wonder. Is it possible for the engine water pump to force water backwards through the heater core and past the heater valve - and if so, how? The one thing I didn't check through all of this was the Aux Pump. Do you suppose if it isn't pumping towards the valve that it can allow water to circulate backwards?

For now the symptom has a band-aid (well actually two) on it. So, a final thought and question for this post is; I saw somewhere on this board that someone had come up with a vacuum operated heater valve modification. I'm sure I could find it by searching, but have any of you read that post/thread and would you recommend that mod? Or should I just spend the money on a new pump and heater valve?

Thanks again guys for all your help, thoughts, suggestions and diagnostics... I think we're almost there!

Regards,
Michael B.

Oh, Brewtoo, almost forgot - the side vents I determined a while ago also blew warm/hot air. I just didn't update ya.