Climate Control diagnostics - PeachParts Mercedes-Benz Forum

mikesan152 · #1 05-23-2007, 10:57 AM

Let me start by thanking all those who have already contributed to the wealth of information available on this forum. In diagnosing the center vent problems in my 87 SL, I have found a number of problems.
1. There is a vacuum leak in the defroster pod. I determined this with a vacuum pump and gauge with vacuum applied directly to the line which attaches to barb 2 (on R Smith's Diagram) of the switchover valve.
2. Vacuum only appears at barb 1 (floor pod) of switchover valve, despite selecting different options on the climate control push-button unit. The only buttons that seem to make a difference are the off and defrost buttons, but these only affect the blower motor. The switchover valve does not react.
My questions are:
1. How does one diagnose between the switchover valve and the push-button control unit? (Can it be done w/o an expensive tester using jumpers or the like?)
2. What parts are more prone to failure in these two devices? Rebuildable?
3. Can the pods be rebuilt or is it more cost effective to replace them?
4. Where can I find the little foam tube that connects the interior air temp sensor in the dash to the system?

Thanks again for all the posts on this subject. I explored all I could find before I posted. It's possible that I just missed it...(dain bramage)

Mike

TX76513 · #2 05-23-2007, 12:09 PM

1. Testing the switchover valve you are evacuating from the top nipple. If the vacuum maintains all is good if the pressure increases the valve is defective. The electrical function test should read zero when valve is open
2. Viewing the forum it appears pods fail more frequently than switchover's
3. That's a great question - don't know they are pricey
4. I believe Phil here at Fastlane can send you in the right direction for that.

SunGuy · #3 05-24-2007, 01:30 AM

TX76513,

George Murphy at Performance Analysis can get you the pod 'innards' and they are very inexpensive. He can be reached at perfanalysis@comcast.net

As suggested, Phil can get you the foam tube to connect the cabin vent to the system I'm sure. In my case, replacing disintegrating foam with more foam didn't make sense to me, and since I'm not an MB purist, I cut a short length of 3/4" plastic tubing I got at the Depot, installed it, and it hasn't moved or disintegrated in the 10 years since I did that.

Have Fun-

Bob

mikesan152 · #4 05-24-2007, 09:09 AM

Thank you both.

TX76513, my switchover valve has no top nipple. Vacuum comes in from the left side and is distributed among four nipples along the front. No matter what the climate control buttons are set at, vacuum is only and always present at the nipple for the floor pod. I know the "when in doubt, swap it out" approach, but I was hoping to go about it more scientifically. (That means I don't wanna spend money for the wrong part!) I was hoping there might be a simple way of jumpering the module to verify operation or defect.

Thanks!

TX76513 · #5 05-24-2007, 09:26 AM

Quote:

Originally Posted by SunGuy

TX76513,

George Murphy at Performance Analysis can get you the pod 'innards' and they are very inexpensive. He can be reached at perfanalysis@comcast.net

As suggested, Phil can get you the foam tube to connect the cabin vent to the system I'm sure. In my case, replacing disintegrating foam with more foam didn't make sense to me, and since I'm not an MB purist, I cut a short length of 3/4" plastic tubing I got at the Depot, installed it, and it hasn't moved or disintegrated in the 10 years since I did that.

Have Fun-

Bob

That is a fantastic piece on information thanks. Those Pods are North of $60

Mike - sorry about the single nipple was (hoping) their was some similarities between 126 ACC's

mikesan152 · #6 05-24-2007, 01:47 PM

Actually, I made out alright. I pulled out both the climate control selector unit and switchover valve assy. (If anyone needs the pin-out of the connector, I have it.) It's easy to test using a vacuum pump/gauge and a small battery charger. I was able to actuate all four vacuum control relays, so that tested good. Inasmuch as I was doing all this through the glove box, I found it was much easier to put the holding screw back in first, and then notching the switchover assy so it would slide over the installed screw. Then I just had to tighten it.

The climate control selector was a bit tougher. However, after pulling the bottom cover off I could see several questionable solder connections. I re-soldered about a dozen pins and put it all back together. It works! I still have to deal with the leaking defroster pod. I also conveniently forgot to replace the aspirator tube (yeah, I'll use something more durable when I do fix it). BTW... I am happy to announce that I am the proud owner of a cracked heater box. I think it will have to wait until winter. I can yank the dash and fix the defroster pod at the same time. All in all, it wasn't too bad except that the rest of the car seemed to always be getting in the way.....

Thanks again for all the support.

Walrus · #7 05-24-2007, 08:56 PM

mikesan152,

May I invite you to navigate to: http://users.adelphia.net/~rmsmithco . Heater box repairs need not be too daunting. I logged about 17 hours on my project.

Good Luck!

Roncallo · #8 05-24-2007, 10:01 PM

Quote:

Originally Posted by mikesan152

Let me start by thanking all those who have already contributed to the wealth of information available on this forum. In diagnosing the center vent problems in my 87 SL, I have found a number of problems.
1. There is a vacuum leak in the defroster pod. I determined this with a vacuum pump and gauge with vacuum applied directly to the line which attaches to barb 2 (on R Smith's Diagram) of the switchover valve.
2. Vacuum only appears at barb 1 (floor pod) of switchover valve, despite selecting different options on the climate control push-button unit. The only buttons that seem to make a difference are the off and defrost buttons, but these only affect the blower motor. The switchover valve does not react.
My questions are:
1. How does one diagnose between the switchover valve and the push-button control unit? (Can it be done w/o an expensive tester using jumpers or the like?)
2. What parts are more prone to failure in these two devices? Rebuildable?
3. Can the pods be rebuilt or is it more cost effective to replace them?
4. Where can I find the little foam tube that connects the interior air temp sensor in the dash to the system?

Thanks again for all the posts on this subject. I explored all I could find before I posted. It's possible that I just missed it...(dain bramage)

Mike

1) the switch over valve can be fully diagnosed with a 12V power source and referance to the wire diagrams to see which pins actuate which valves.

2) I havent personally seen a switch over valve fail. On the other hand, I dont belive you will find an SL with an original push button because they fail all the time.

3) Pods can be rebuilt and the parts are available from both MB and the aftermarket. I dont recomend pod overhaul only because they are located in very expensive real estate when it comes to replacement. In fact because of the difficulty of the location I would only recomend using genuine MB new pods for at least the leg room centervent and defrost pods. The fresh air flaps are the only pods I might consider rebuilding.

4) The foam tube is available from any MB dealer or right here at Fastlane. It is expensive Like $40.00 and most people elect to repair it with a piece of 5/8" heater hose or similar.

John Roncallo

mikesan152 · #9 05-25-2007, 10:02 AM

Actually, I've been to your site. That's why I knew I should look for the crack. (BTW, I found the vacuum layout diagram most helpful.) I would tend to agree about just replacing the pods. They aren't that expensive.

I noticed that the Recirc switch still seems to have no effect. Is that a common failure item? It's easy enough to verify, I suppose.

Thanks for your input and contributions to the SL brotherhood! You and John and others did a great job.

Mike

Roncallo · #10 05-25-2007, 05:26 PM

My recirc switch had no effect when one of the relays on the push button control went bad. I couldent find a replacement relay so I bought a new controller, problem fixed.

John Roncallo

Quote:

Originally Posted by mikesan152

Actually, I've been to your site. That's why I knew I should look for the crack. (BTW, I found the vacuum layout diagram most helpful.) I would tend to agree about just replacing the pods. They aren't that expensive.

I noticed that the Recirc switch still seems to have no effect. Is that a common failure item? It's easy enough to verify, I suppose.

Thanks for your input and contributions to the SL brotherhood! You and John and others did a great job.

Mike