looking for part # and process to replace the A/C actuators

[ronin]

I have a 94 c280 which has had an A/C issue for well over two years now. The system has been checked several times. A vacuum leak was suspected and some module that had vacuum hoses connected to it located in the engine compartment was changed because it had a hairline crack in it. It did not solve the problem. The symptom is still the same, start the car, start A/C, air blows nice from all vents and then air is directed to the windshield defrost after a few moments of running. Air is also cut from the lower blowers but air from the side vents is fine. I should also note, even though the air is directed to the defrost, it is always cold, the windshield frosts where the deforest vents are located.

On occasion, the air will blow back through the center vents for short period of time and then cut off again, redirecting to defrost. When selecting the various air distribution buttons, you can hear clicking like something is being switched but the air is not redirected. Air only comes in from the side vents and the defrost, nothing from the center of lower vents. If I hit the EC button on the controller, Air will be redirected to the center and lower vents but then warms up. Once I turn off the EC, the air stays on the center/lower vents for a short time then defaults to the defrost. This happens every time I hit the EX button.

I've been searching this and other sites for information on this issue and it seems that the issue is somewhat common and everyone points to a crack in a vacuum line or the two actuators next to the glove box, the rubber wearing out due to use. since it doesn't look like it's a bad vacuum line, I'd like to replace the actuators. Does anyone know the part number to those actuators and the procedure to replace them. Also, any special tools need for the job. Lastly, is it recommend to replace the vacuum line while doing this procedure as a precaution.

Any and all input to this issue and request is welcome and appreciated.

[98_Benzo]

Alright, I am throwing out a couple ideas for you that you might want to look into. First, when you are talking about "A/C actuator" what is the actual technical term for that part? I haven't heard of an "A/C actuator", but there is a couple of diaphrams in that area that you are talking about. Next, I don't think that, the hoses and all that are your problem. Have you took the head unit in and had it looked at? Try pulling out the headunit if you have the keys and making sure that there are no wires that are crossed. I am looking at your car as being the first year the W202 came out, so it is getting up there in age. Have you ever removed the headunit before? Is this the stock headunit or has it been replaced before? The problem definitely sounds like a headunit problem and I would go get that checked before you start putting a hundred dollars here and a hundred dollars there on hoses and stuff. Well, I hope that helps out, let me know what happens with that. If I am completely off on my theory tell me what it was, so I know for next time.

[ronin]

Hi 98_Benzo,

Thank you for your time to respond to my issue. I want to state that I'm totally ignorant to all aspects and terminology relating to cars, outside of the obvious terms such as tire pressure, gas cap, ignition, automatic and other high-level terms. Regarding your questions:

Q1: "First, when you are talking about "A/C actuator" what is the actual technical term for that part? I haven't heard of an "A/C actuator", but there is a couple of diaphragms in that area that you are talking about."

A1: Actually, I don't know if I'm using the correct terminology for the components in question, I read a few posts from a few sites and the parts in question were being referred to as actuator, so I borrowed the term. From your description, the parts are the two diaphragms next to the glove box.

Q2: Have you took the head unit in and had it looked at? Try pulling out the head unit if you have the keys and making sure that there are no wires that are crossed. I am looking at your car as being the first year the W202 came out, so it is getting up there in age. Have you ever removed the head unit before? Is this the stock head unit or has it been replaced before? The problem definitely sounds like a head unit problem and I would go get that checked before you start putting a hundred dollars here and a hundred dollars there on hoses and stuff.

A2: I'm not sure what a head unit is, so I'm not sure how to answer this question about it being checked or replaced. Also, even if I were able to remove the head unit, I wouldn't know if a wire was crossed or pulled out. Any help with this, is appreciated.

I can say, I have two keys that can remove the radio, which is the stock radio with the cassette. If your term head unit refers to the radio, how can it control what's going on with my A/C center vent air issue.

Lastly, you can see why this issue has been around for over two years, I'm clueless and mechanics key into that and all I wind up doing is paying without the issue being resolved. That's why I'm looking for help from the Do-yourselfers on the various MB sites.


Thanks again for your time and help

Ronin

[98_Benzo]

Alright, after my last post, I started thinking about it. You don't have the same "headunit" as I do. If you look at the 96 to 99 W202's there is another display unit above the stereo that can be pulled out with the keys that you pull the stereo with. On yours, you have the buttons that are above the stereo that control your A/C and heating, right? Okay, the headunit is a box that looks kind of like that back of a stereo, it will be located behind all the buttons on your dash. So, you are going to have to get behind the buttons, it will be right above your stereo, but behind the woodgrain. If you feel uncomfortable about pulling that all apart yourself, you can take it to a dealership and they can check it without it being pulled for a reasonable price (they might check it for free, don't quote me on that, but they should). Alright, if you do this on your own, to make sure no wires are crossed, look at your wiring and see if any of the wires are showing copper, if they are your going to want to wrap the copper area in electrical tape. Alright, I am not going to feed you to much info all at one time, because it will be hard to take it all in at one time. So, do those things above first and let me know. Good luck!!

[ronin]

Thanks for clarifying the head unit . Yes, mine has the temp display in the middle and buttons on both sides, the right side to select the fan speed and air flow direction and the left side controls the power , rec, E/C and some other stuff.

Regarding the head unit, I don't know if it's been tested completely or even replaced for that matter. I'm the second owner of the car and have had it for 5 years now. I can say since I had it, it was looked at (so I'm told) but not replaced. I cant say if the original owner ever replaced it.

Regarding getting in and taking the head unit out, I can do that. I'll see if any wires are showing / out of place and let you know. I wont be able to get it until Sunday, I'll update on Monday.

One last question regarding the head unit, when the air redirects to defrost, I can press the air direction buttons and you can hear switches activating but the air does not redirect. Just the mere fact that the unit is sending the commands doesn't it mean that it's working. Also, I do hear some sort of pump in the trunk every so often. It runs for a while and then cuts off and then cycles back on. not sure if that means anything.

Ronin

[98_Benzo]

The noise in the trunk, is that when the car is running? If so, that is your fuel pump, it is supposed to make that noise, German cars are very popular for having loud fuel pumps. As for the A/C it should all still work and make noises, but if something is loose on the inside it can make it so some functions don't work. Also, like I said before, crossing wires can do that also. I will wait to hear from you on Monday then, good luck again!!

[ronin]

98_Benzo,

the noise in the trunk is once the car is started and is coming from the right passenger side of the car. Anyway, you can always hear it cycling. sometimes it keeps up for minuets at a time and then stops and kick back in, in no specific interval.

Regarding the air flow and head unit, it seems odd that considering how over engineered everything is with MB that something would come loose, more so in a unit that doesn't have any moving parts, just switches and impact only part of the air flow operation. Anyway, not that I know what I'm talking about, just thinking out loud, besides, I'm sure anything is possible. I'll take a look and update you. Thanks for your continued support.

Ronin

[98_Benzo]

The noise that you are hearing in the trunk is more then likely your fuel pump, it might be going bad. You might want to get it checked out!! As for the A/C, it doesn't need to have moving parts to go bad on the inside, you could fry wires on your board or there could be corrosion on your board from being old. There are a lot of different things that could go wrong on the inside. For instance my auto dimming mirror broke and it wasn't from me adjusting my mirror, it was a little piece of plastic chipped off from the mirror (on the inside of the casing for the mirror) and it caused the whole thing to break. Luckfully, I had a paperclip and some tape handy and we opened up the mirror and fixed it for now. Anyways, I hope I am helping you out, if not just tell me so.

[JRE320]

Are you the first owner of the car? Did you change your engine wiring harness? Wiring harness is one of the cause of your car to go nuts on your electricals

[ronin]

Hi all,

First, JRE320, I am the second owner of the car and I don't know if the wiring harness has been replaced. So far, since I purchased the car over 4 years ago, everything has been running fine (outside of normal ware) except this nagging A/C air flow issue. The air is cold, just that it gets directed to defrost and the side vents. Also, every so often it will toggle back to the center vents. However, the defrost is the most common direction.

98_Benzo, I was able to take out the head unit yesterday, boy talk about over engineering, and it looked OK. The head unit is encased and has two wire connections on each side, I didn't see any open or loose wires. I opened the unit and didn't see any burn marks or corrosion. I put the unit back and the system operated as before.

Ronin

[98_Benzo]

Hmmm......well, without being there this is a little difficult to tell what is wrong. I am sorry I couldn't help you at all, if I come up with any other ideas, I will post them up here for you. Wish you luck on getting that fixed!!!

[ronin]

98_Benzo, no worries and thanks for your time and suggestions. Though the issue has not been identified yet, you helped jump start the thinking process to getting this issue identified and resolved.

Ronin