[Sinned420]

Does the duo valve stay on when you turn off the car? I still hear it buzzing quietly sometimes. When I unplug the plug in the picture, it stops (well obviously), but I'm not sure if it's suppose to. I'm having issues with my duovalve so I'm just curious.

 

[drcharlesatlas]

No, the duo valve shuts down when ignition is turned off; however. there is an auxiliary water pump that is a part of the duo valve component that may continue to run for a short time, depending on the high temperature of the coolant. This information applies to
the S500, but may be different from your 420, but I doubt it. The picture that you show is the auxiliary water pump.

 

[Fluteguy]

I went through the same questions when I first got my W140. It's the aux. water pump and it runs after you shut the key off to cool the engine. It should shut off after a certain time (not sure how long).

Its normal

 

[Sinned420]

You're right. I meant that pump but said duo valve since they're all together. I guess it makes sense it stays on when car is still hot. My guess is it stops at a certain temp.

I just ordered a new unit, I hope that's my problem. I can't confirm that I have stuck valves which causes my side vents to blow hot air until the new unit arrives so I could open and examine the old part.

I've gotten error codes for short/open circuit in the valves and the pump as well as pump being overloaded and aux fan short/open circuits. Quick look at the wiring and it seemed fine with no insulation issues like the engine harness. I will look harder and trace it later. I'm afraid the wires are part of the huge body harness...

 

[kcscout]

I suspect that I have a bad duo valve from reading these posts, but I don't know where it is on the car. can you please tell me or better yet post a picture of the valve on this thread.

 

[lcmlee]

You can check the temperature of the incoming and out going temperature of the dual valve. Go here for how to check K6JRF Auto Page

K6JRF is probably the best source for AC troubleshooting.