LawRens

Calling upon the veterans of the w202 architecture here; while I have moderate knowledge for repairing and maintaining most parts of a c43, I have almost no experience regarding its HVAC system.

First off, when the fan is on the vents blow constantly out of the defroster, the left and the right side. The center vents have nothing coming out of it. If I am not mistaken the vents are controlled by vacuums and hoses, and I have a feeling that a hose has become brittle and broken off; however, I have absolutely no idea where those hoses are located. Can someone enlighten me (pics definitely would help) as to where I can find the connections for vent control?

Second, the A/C is no longer operational. It could be one of the following reasons and I need help in identifying where the problem stems from: Freon levels are low, A/C evap temperature sensor is dead, AC condenser is dead, or maybe something else I am not even aware of. I did check out the climate control diagnostic (actual values) while the car was on, and the refrigerant pressure in bar was 8 bar. The evaporator core temperature sensor was somewhere around 170 degrees fahrenheit.

I have previously searched this and other forums for similar issues but did not find find the answers I needed. Advice from the experts would be much appreciated.

nd4spd13

Vent issue is somewhat common. No telling which vacuum tube it is though. If you remove the passenger side knee board, that's where the actuators are located to split the vacuum for each vent, I'd check there first. I had this issue and the tube that was undone for me was actually the white one that plugs into the throttle body area. You'll see it under the little plastic cover on the passenger rear side of the engine, then it runs into the fender, then into the fire wall through to the pass. foot well.

Hope this helps!

503C43 ////AMG

Check post #13

https://mbworld.org/forums/c36-amg-c...diagnosis.html

LawRens

Thanks for the tip. When you refer to passenger side knee board, do you mean the board (held by three screws) that sits below the glove compartment? I opened it up, but was not sure what/where the actuators actually were, so i boarded it back up. Funny, considering now my fan doesn't work at all Going to spend all tomorrow trying to fix that now WITH the vent control...

Thanks for the link. I know the evap temperature is too high, but now I need to wait for someone to drop by so i can test to see if the compressor shuts off.

And I have a 6 hour road trip next week

Sulaco

I'd say a very large portion of flow direction issues are the vacuum bellows in the dash that are controlled by vacuum. The presence/absence of vacuum makes these pods move the levers that open/close the different valves. Huge number of w202's have these pods fail, including my previous 1994 C280.

I believe one or two of them can be replaced if you're careful and feel like removing steering wheel, both knee bolsters, and the entire dash face and trim (radio, ccu, etc). The real fix is removing the dash and replacing the pods. Not a job for the faint of heart at all. Took me 4 whole days to replace the 2 failed bellows in mine, but it restored all proper flow.

I also had to replace my AC evaporator. Pray to the mighty Lord that you do not have to do this. Aside from replacing the dash, you have to evacuate the system and plug it ensuring no ambient air gets into it. You have to drain coolant because the heater core is coming out, too. Then disconnect an absolute nightmare of vacuum hoses, wires, cross members, and irreplaceable plastic clips and snappies all over the place.

Then you get to put it all back together! Most shops charge $3k for this job.

Diagnosing no-cold-air is much easier and cheaper. Step one is to perform diag using the built-in method on the ccu. That will tell you status and readings of sensors, pressures, RPMs of compressor, etc. Assuming the CCU is functioning correctly (it usually is) it should tell you all you need to diagnose.

If not, you need to get some manifold gauges and hook them up to test the pressure yourself.

I can explain the variables at that point, if it gets to that.


God speed.

nd4spd13

Yep that's the one.

Sorry it's not a great shot, but hopefully you can see here how just above the foot vent there's a collection of vacuum tubes. I figured that's the best place to start, as I'm pretty sure that's where they go to the individual "pods" for each vent. Then I imagine there's another one of those on the drivers side. This piece I'm referring to acts as a distribution block from the big green tube coming through the firewall on the pass side and the air vents.
Are you saying your fan stopped working after the kneeboard removal? It's the big plastic bit under there with two clips, you probably just bumped the plug when you were down there

LawRens

I certainly am hoping that the vacuums have just fallen out of place. I am definitely not in the mood to begin ripping my dash apart to replace a few vacuum hoses.

Yeah, I realized that the plug fell out of place when I was prying around. I popped it back in and voila, the fan began to work again.

Thank you very much for the photo; I will be tinkering with those vacuum tubes tonight in hopes of getting the center vents to start blowing air again

Sulaco

Also check the vacuum Junction thing under the hood. Right or passenger side under the plastic cover that protects electronics. Is a plastic thing with like 6 vac lines hooked up. Make sure it's not cracked or disconnected. Inspect around the little ball bearing

LawRens

I searched around where you referred to, but all I found was the ECU under the cover Refer to the attached pic: is the cover in the red circle what you were talking about?

Edit: I think I understand now; it seems that the US spec c43 will not have the vacuum distributor under that cover, but behind the passenger side front fender liner... I'll be checking this out as soon as I get back. Fingers crossed that it's there, and that the hose just fell out of place.