How is A/C control panel supposed to work - PeachParts Mercedes-Benz Forum

cool123 · #1 10-02-2007, 08:00 AM

I've asked questions without reply, so I'll try again.

1) I just replaced the vacuum pod for the defrost vents

2) When I press the "EC" button only air comes out of the center vents. Works like it should!!!!

3)When I press the center button for vent air only, I get leakage through the defrost vents, this is not right.

The vacuum pod is new, and I've already tried another A/C panel.

Is this a switchover valve problem????????????????????????????????????????

mbdoc · #2 10-02-2007, 08:24 AM

What year & model car???

TROVERMAN · #3 10-02-2007, 09:20 AM

If its like the 124 model with a row of square buttons, a temp dial, and 3 fan speeds, it should work like this: Defrost button automatically operates maximum heat regardless of temp dial setting. Heat to windshield and outer vents. Up-down button splits heat to windshield, outer vents, and floor vents. Temp and speed dependent on dial and fan buttons. Center button (most commonly used) supplies heated air to outer vents, floors, and a slight amount to windshield. Heat is only supplied if interior is cooler that temp dial setting or dial is set to full heat. Cooled air on this setting blows out all four front vents and a slight amount to windshield. Cooled air is only supplied if interior is warmer than temp dial setting or if dial is set to maximum cool. EC button works exactly like the button just to the left of it, except the AC compressor is not turned on. Air is exterior air. 0 button allows some convection heat.

Hope this is helpful.

cool123 · #4 10-02-2007, 09:57 AM

its a 91 300E

I can't believe that when the center button is pressed its supposed to leak some air through the defrost.

When the EC button is pushed the vaccum valve has vacuum and closes all the way.

I do not have full vacuum this valve when pressed.

The whole problem is the windsheild frosting up because it will not close the valve when the center button is pressed in.

Surely Mercedes is not that stupid. Having replaced the vacuum pod under the dash, and tried a new panel, I know only one thing.....the defrost vent valve is not getting the vacuum it should when the center button is pressed, but when EC is pressed, the valve closes off all defrost air.

TROVERMAN · #5 10-04-2007, 08:11 AM

On the climate control system I am not that knowledgeable in the technical aspects of operation. What I have told you is straight out of the owner's manual of what the system should do, and that is how mine works.

In heat modes, no air or very little should come from the center vent ever. With the center button pressed, regardless of heating or cooling, air will go to the side vents and some air is leaked to defrost. The AC is always running (heat or cooling) with the center button pressed as dried air defrosts better and removes condensation that fogs up the windshield from inside.

Does you recirculating button work right? If that is stuck on your windows will fog up pretty quickly.

I guess I am fortunate in never having any problems with the system on our '95 ever. It seems to work quite well, especially in terms of the accuracy of the interior temp. It works considerably better than the digital dual zone systems in our Range Rover / Land Rover and VW.

Good luck

cool123 · #6 10-05-2007, 02:22 PM

yea, I haven't bought a manual.

Maybe the recirc valve is the problem.....

but at night driving.....that leakage from the defrost vents...just constantly fogs up the front windsheild, and I'm constantly having to turn on the wipers.

ofcourse in the daytime...its not bad, unless you have a rainy day...then its again.