1995 SL500 Climate Control - Benzworld.org - Mercedes-Benz Discussion Forum

Ozzie Rob · 11-15-2012, 10:01 PM

Hi all,
I am new to the forum and this is my first post.
I have a 1995 sl500 100,000 km in show room condition. The problem I am having is when I put the air con on, I get hot air out of the two side vents and unless I press the blueg button in the center vent the air will be hot.
If I switch off the two side vents I get cold air out of the center main vent, but it seems like cold air comming over hot air. Please help.

Thanks, Ozzie Rob

RKH · 11-16-2012, 08:16 AM

Have you try the RED button ?

Ozzie Rob · 11-16-2012, 03:15 PM

Hi RKH,
Yes I have tryed the red button and that makes hot air come
out of all vents.
When I hit the blue button I get cold air from center vent and hot from sides.

RKH · 11-16-2012, 03:54 PM

Red button ON routs air through the heater core to the center vent.
Blue button ON routs outside Air to the center vent.
Both are for overridding the automatic climate control ssystem and direct cold/hot air to the center vent only, and has nothing to do with the side vents.
So leave them both OFF for automatic operation.

In automatic mode, the system controls air flap/doors to blend cold/hot air to the desire temperature, and those air comes out of both side and center vents (unless they are shut off by the thumb wheels).

From what you said, seem like you are getting hot air all the time, no matter AC is ON or OFF. Chances are you have a vacuum leak that the (vacuum operated) blending air flap door is stuck on routing Hot air only.

Ozzie Rob · 11-16-2012, 08:03 PM

Any suggestions as to where I should start looking?
Also, I should add that I am in Australia and it is RHD.

aam · 11-17-2012, 10:54 AM

Start with checking the vacuum distributor, located in the module compartment.
It is known to crack around the ball bearing plug.
( Pull tubes with a 7mm open wrench.)

Also the vacuum reservoir.
It will help if you have a vacuum hand pump.
One indication is that the vacuum pump runs on and off for extended times.

Regards
aam.

edcarls · 11-17-2012, 01:09 PM

Quote:

Originally Posted by Ozzie Rob

.... I get cold air from center vent and hot from sides.

I had the same symptoms on a W124 and it was caused by faulty mono valve. I don't know if R129 has the same mono/duo valve. It maybe worth checking if it does.