center vents not working on 560SL

[RickM]

Strife,

Can you take pics of the replacement? This is extremely common and pics would benefit many.

Thanks.

[lynns]

Originally posted by RickM
Strife,

Can you take pics of the replacement? This is extremely common and pics would benefit many.

Please pay attention to the file size limitation of 66 KB. Example: You may need to convert a JPEG to a TIFF to meet the file size limitation.

[Strife]

Center Vents REPAIRED! (longish)


So, to follow up (see previous message), I removed the offending "double" vacuum actuator to the left of the radio. I gained access by removing the air bag/steering wheel and dashboard (I made the tools to remove the dash out of piano wire I bought at a hobby store here, MUCH stronger and thinner (important) than coat hanger.

Something no one has discussed is the strong possibility of cracking the dash (or making existing cracks worse) while removing the dash. I think I may have made some existing tiny cracks worse at the creases where the dash meets the arc of the instrument panel. Be careful to distort your dash MINIMALLY while removing the instrument panel.

Anyway, the pod is held by THREE, not FOUR, speednuts with washers underneath. I pried these off (but I should have removed the rivet first, see later. The rivet is unfortunately flat head towards you. No problem, I thought- I have a super-duper dremel-like tool with a cabled handpiece and some diamond grinders, so I can just grind the top off.

Well, I slipped and I screwed up the actuator arm. The @#$%#$%W rivet, unlike the rest of the piece of @#%$@, is made from some exotic aerospace alloy or something and it was extremely difficult to remove this way. But I eventually did remove it. It has been suggested that removing the radio is better so that you can get at the bottom of the rivet; I can’t argue with this.

In the meantime, what was I going to do on a Friday with this pod with a broken actuator top (I opened the hole so that what was a hole was now an open hook). I cut the broken part off, filed and drilled a slightly lower hole in the plastic. This would have the effect of leaving the defroster slightly more “open”. OK, I thought.

In the meantime, I drilled the hole a little too low and allowed a hold to develop in the white plastic actuator base, allowing air in to the top part of the unit. DAMN IT. So I sealed this off with epoxy putty.

I rebuilt the pod as per the instructions with the rebuild kit. -Make certain- that you photograph or draw the exact relationship of the actuator arm to the speednut stems before disassembly, as well as where the nipples for the vacuum are. I STRONGLY recommend that you buy the $10.00 tool. Disassembly was very difficult even with this tool, and the plastic is that “brittle” kind of plastic.

Both top and bottom rubber was shot; the upper part was actually chewed through and apparently was MISSING PIECES! I noted that there was a white deposit in the unit and I wonder if somehow water accumulates here (it has been speculated that heat alone destroys these units). Anyway, I rebuilt the unit and tested it with my vacuum pump.

The bottom part of the actuator is the LONG throw, and the top is the short throw. The top is also shared with the infamous center vents. The short throw part of the unit hardly moved the actuator arm at all. Because of my unfortunate drilling incident, the top part didn’t want to hold a vacuum forever either (although it was definitely working almost at spec), so I decided to block off this part. Operationally, I think this makes hardly a difference at all. The vast (95% in my case) part of the unit movement is done by the bottom part of the actuator.

Reassembly was a nightmare, because there is very little room to work with. I used an allen head screw and a jam nut. The allen head made it easier to work in there. Getting this right was very difficult and took an hour alone. I had to drill out the actuator arm hole a bit. Make certain that your screw/nut is not so long or sticking out as to catch on the hole in the actuator when it retracts.

While I had the car ripped up, I cleaned and re-lamped the dash, as well as painted the indicator needles.

After reassembly, I was disheartened because the system didn’t seem to work although I had tested 6 of the 7 pods. However, when I drove at speed, the system magically started to work! I assume that more vacuum got things going!

Bottom line:

1. Get or borrow a hand powered vacuum pump (I got mine for $30, and it does a lot of other things too). There is no point on speculating on the pods until you test them.

2. Center vent failure is NOT NECCESSARILY a failure of the inaccessible pod that actuates the center vent!

3. If you want your center vents to operate and you know the top part (ONLY) of your actuator is bad, it may be possible to bypass it via the infamous "golf tee" fix (don't actually use a golf tee).

[lynns]

Thank you for sharing your repair job. You are so right about your concern with regard to cracking the dash upon removal. When my 1988 560SL went in for a cracked heater box warranty repair they cracked the winshield and sent it back to me as if I would not even notice it. Note: They had to replace it at there cost.

This is the second time that I have heard of a self repair job on the center vent actuator where the actuator broke, cracked, or was a real problem. "Strife" spent $30 on a vac pump test kit and $10 for the actuator repair tool and at least $5 for new diaphragms and epoxy putty. A new actuator might cost $65 ??

I am by no means a rich man but sometimes it just pays to have an trained authorized repair shop make the diagnosis/repair.

With my glove box removed. I am so grateful that I paid $80 to my MB repair shop to test the whole system. And $40 to open the center vent. What a savings of time and labor !

[Strife]

Well, on the stuff I bought, I did my brakes, too, and bought the vacuum pump to bleed and drain them-I had the epoxy from this "radiator pre-failure repair kit" I bought from a guy on eBay (this is a copper pipe you mount inside the radiator neck with epoxy so that it is stronger and doesn't break catastrophically when you are driving - can very badly overheat the engine even if you stop right away). Overpriced, but still possibly worth it. I went nuts and bought the tool and enough diaphragms to do all my vacuum actuators, which ran about $60. I've invested quite a bit in tools recently (I had my tools stolen some time ago and figured that I'd never be working on cars again at my age), but, between doing the brakes, shocks,tuneup, all fluids+filters, (best filters,plugs,cap, rotor, wires, brake rotors, pads, rebuilt calipers (3), and new brake fluid) - I'm still incredibly money ahead, and I now have the knowledge and the tools that I need to fix other things as they come along. I plan on owning this car for a long (>10 years) time. I guess it depends on what you think that you can do, and how much you value your free time vs how much money you make. I'm a high tech worker who actually still has a job; I could have afforded to pay someone else to do this stuff, but it KILLS me to pay someone to do something I can do myself, even if isn't the best use of my time. This may be a character flaw, or it could be that I am a cheap a**.

BTW, this car SEEMED like a "creampuff" when I bought it...God!!!

[yeldogt]

I know for a fact that when MB fixed my system - replacing the unit just to the left of the center vents -- they did not have to remove the dash -- it all went through the center opening!

[ML320]

The center vents in my '81 Euro 500 SEL (W126.037) stopped blowing cold air and after troubleshooting it with the help of the diagram posted earlier in this thread, I found an easy fix. An original vacuum hose rubber Y connector leaked. It was made by WOCO, MB part 1170780145, Mercedesshop has the replacement in stock:

Item Number: D3011-73182
Main Category: MERCEDES BENZ
Sub Category: Vacuum Hose Connector
Description: Vacuum Hose Connector
Manufacturer: AAA:LEM
List Price: $5.25
Your Price: $ 3.26
Core Price:
Weight: 0.010

Quantity Available: 9

[sshankman]

Hi all

I have the familiar problem of not having air coming through my center vents. Today I was looking around at the vacuum lines and trying to follow this diagram of the climate vent control vacuum system, but I am confused. If you would be so kind as to take a look at this diagram, maybe you understand it enough to help me get through this.

I want to understand actuator 38, which has two vacuum connectors. What is the side connector (hose labeled "rt/hbl", which I think is German for Red/Light Blue) for? It leads to another device (no. 45a), which connects to the line labeled "rt/sw" (red/black in German), and we cannot find any line with black on it.

There is also a kind of junction block (no. 16/15/13/14 in diagram) which I don't understand. There are two connectors on the top with "-" and two with "+". Does that mean negative and positive pressure? And, there is a common line (rt/gn, or red/green) that leads up to part 35. Is that where the vacuum is generated?

Finally, on my heater box, I noticed that there is an inlet on the front, to which a short red/yellow hose is attached. This hose leads to an actuator (I believe it's the defrost vane actuator) right next to it through a 3-way connector, the third hose being red and white, leading back across the dash to the junction box behind the glove compartment.

I am more or less mechanically inclined, and I'm led to believe there's a leak or a faulty actuator, but to diagnose it properly I would like to understand the workings of the system so I can test out things. For example, we directly connected the red/green hose right onto the red/white one leading to the defrost actuator, and it closed it for us. Then we manually opened up the center vent, and we have air, but of course this is no permanent fix.

Thanks for the help! Look forward to trying to fix this!

[yeldogt]

Hi

I will try to help with this!

13 to 16 is the vac control box -- it takes it orders from the climate control panel and just sends the vacuum to the corect actuators.

45 is nothing more than a one way vac valve -- to make sure the vac does not go in the wrong direction.

The two 42's and 43's are the fresh air vents that open and close for outside air -- they are powerful (double) to over come the air pressure at high speeds when you want to close off outside air.

39 is for the lower heater vents

40 is the unit in the heater box for the center vents

38 is for the defrost vents -- it is a two position unit -- it also moves both of the defrost flaps. When the unit is in bi-level mode the vac hose on the side of the unit is active -- it only moves part way. This way with the heat vent open you get the bi-vent. If it went all the way open, all the air would just go to the defrost.

Only 38 is a two way unit -- all the others are just open or closed.

38 is used all the time and also moves two vents -- it often is the problem. if it has a leak no vac will flow to 40. If you remove the lower hose from 38 it should have vac -- connect this hose to 40 to see if 40 will now work.

If 40 is the problem and does not open when it has vac -- this is a bigger problem as you can not get to the unit to fix it. The layout for this part is very bad.

Many things that can go wrong -- the rubber hose connectors can go bad. If the system is working in some modes you know you have vac -- if it is not working at all then the main hose is off someplace or the one way valve in the main hose could be bad.

Let us know what is working and what is not -- the above is just a start.

The replacement units from MB are stronger now than the original - if 38 is bad get the new unit.

[sshankman]

Hi! Thanks so much for your post! That is incredible information! I have a few further questions if you don't mind.

I bet you are right about the problem we are having. I suspect that it's 38. I will have to test 40 to see if it works. The question is: How do I find the connector for 40? I noticed that there is a connector on the front of the heater box, but I think there is another connector below the box too. From what you say, I think the front connector (red & yellow) must control the heater vents, so the connector for 40 must be somewhere else on the box.

We noticed that there is vacuum but I am not sure how much there should be, and it's possible that some is leaking somewhere.

Also noteworthy: the front of the heater box, visible from where the ac controls and radio are, was cracked and a small piece (the piece with the rivets) was completely broken out, and it would move up and down when we changed modes on the climate control. When we found out how much it costs to replace a heater box, we repaired it by pulling the broken bit, which had gone inside the heater box a fourth of an inch or so, back out as far as possible, and then sealing it in with a healthy dose of epoxy. Now, it's pretty secure, but it is not completely flush -- it is actually about 1/8 of an inch inside the heater box, as that was as far as we could pull it out.

Thanks again, and we really appreciate you helping out.

[yeldogt]

From what I can remember the heater control is down lower and you can see it -- I think on the passanger side of the car.

The center vent actuator hose is up and to the left -- you can get to it from through the ac pushbutton panel. I think the vac tube just comes out of the box. It must be close to 38 because I remember using the vac line from 38 to test 40.

The mounts for 40 are rivets - you can see them from the front -- the mount for 40 can snap the plastic box. I think I was told that the center vent can stick and the control can then snap the box at the rivets. I would first try to get some vac to 40 and see if it works and if it does work -- make sure that it works without binding. Then I would plug up the two lines to 38 and see if the system works - this will tell you if 38 is the problem. When the system is tight it will work with the engine off after sitting for quite a while.

If any of the parts are working you have enough vac to test it.

You may have a center vent control that broke off at the rivets -- the reason you could not pull it out is that the spring is quite strong on the unit. From what I can remember you can move the center vent to see if it is binding -- I do not remember if I used a stick or I got to it through the glove box -- I do remember that the rubber duct to the center dash vents had come off on one side (blowing air on the dash sensor) and I went through the glove box area to fix that. Make sure you do not hit the underside of the sensor on the top of the dash -- the wires to it are in this area and can come off -- the system will not work if the sensor is moved.

[sshankman]

Thanks for the reply - very helpful.

I've checked the temperature sensor and found that the wires are still solidly connected to it. Incidentally, i recently replaced the rubber tube that connects the sensor to something under the dash. The spongy section of the old tube had disintegrated, so a new one was in order. Not sure if the replacement has something to do with my problem.

This morning, after manually opening the center vents, I was able to get some moderately cool air coming thru the vents. It was enough to keep the cabin comfortable in the 100 degree phoenix heat. But later in the afternoon, the outside temperature rose, and then the air was blowing hot - very hot. I checked the compressor and found that it wasn't engaging. So now, instead of jumping to get a replacment, i'm wondering if any of the vacuum problems could be the cause of the compressor not engaging. I may be low on freon as well, so that could cause this problem.

As for 40, which apparently has something to do with the broken heater box (it broke right at the two rivets), the only way to check or service it is to completely dismantle the whole dash? When I manually move the center vents, they don't bog down at all - they move perfectly smoothly. This should indicate that things inside the heater box are ok, right?

And finally, once the car is turned off, there's no vacuum left in the system, even after a quick restart. This leads me to believe that there's obviously a leak somewhere.

Thanks again for the help. Slowly, but surely, i'm going to figure this thing out and fix it!

[yeldogt]

I just noted the location of the temp sensor so that you woud take note of it when working around it -- if it moves or the large oval rubber tube to the center vents comes off the system will not judge the inside car temp correctly. The tube you replaced sounds like the suction tube for the sensor that makes sure cabin air is always flowing over the sensor.

If the center vent flap moves it just indicates that it is not binding - the actuator may still be bad. It should close again after you opened it -- it will only open when vacuum is applied. If it is opening and not closing then this is your problem.

you need to get inside and test the two actuators to see what is up with them -- since it is not holding vac then most likely one or both has a rip in the bellow.

You more than likely do have a loss of freon or you may have an electrical problem - there is a fuse for the compressor -- and it does go bad. Any number of problems can cause the compressor to not work.

After you get the system working you can check the water valve -- if it sticks open the heater box will always be getting hot water.


good luck -- the climate control system on the 560 is a mess -- a manual system would have been much better for the car.

[lynns]

I am finally ready to pay the price to get my A/C vents working through the center again. Last year, 6/04, when I priced it they told me $1275. That included removing the dash, sterring wheel, etc. and replacing all 7 elements and repairing a cracked heater box. This year it's $1700. They will not do it any other way but what they consider to be the right way. I honor that but cannot afford it.

I really don't want to remove the dash. I understand that it can crack even if the car has been in the garage and not out in the sun a lot.

I called another repair shop today to find out that they where currently repairing another 560SL and invited me to come by. The mechanic had the consol and tunnel removed, glove box, radio, etc. so that you could see the center elements and the cracked heater housing (common problem on 107's). He was going to epoxy the heater housing and replace a couple of elements. He said it was about two days of work. They did not have a finalized price as yet to give me. So I will call them and start researching a couple of shops in my area to do the job without pulling the dash.

I noticed that when you had yours done it was about $400. I live in Newport Beach, CA where everybody has MB and people have money that I currently don't have.

What do you think the job should cost in my area?

Thanks for your reply,

[lynns]

Well I finally had my center vent acuator replaced and cracked heater housing (that rattled) repaired (not replaced). I had it done at an independent. He replaced the actuator and the cracked housing threw the center console at a cost to me of $450.00. Everything seems to work just fine after about 2-3 months now.