Hello hopeful someone can help me with this problem. I have searched the form and have found some good information, but I am not sure that it is relevant to my problem.

I have a problem with the HVAC system in a 96 S320. I think I have narrowed down the problem which is related to a vacuum leak. The vacuum line that feeds into the switch over valve is the same amount of vacuum as other vacuum lines coming out directly from the engine. Under acceleration the vacuum line that attaches to the switch over valve drops to 0. Could this be a problem with the vacuum reservoir or maybe a check valve?
Also, if anyone knows where the reservoir is located? Do I have to take the front wheel housing out in order for me to access it? Before I bought the car the HVAC system never worked correctly, I am not sure if the vacuum lines on the switch over valve are in the right port, I have looked on alldata and the picture of the switch over valve is different from what I have in the car.

Does anyone know the correct color vacuum line to port into the switch over valve? Also I am having a hard time finding information on which vacuum line goes where on the PSE pump. My main concern is the part that is associated with the HVAC system, I think it is the transparent line, so it should go to p-? There is also two transparent lines that connect into one, could this be for the hvac? Where should they go?

Thanks in advance!

The plastic vacuum distributor could be leaking, has built-in check valve.
Or the vacuum storage tank under the right fender could be the issue.

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MERCEDES Benz Master Guild Technician (6 TIMES)
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190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
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The distribution block is under the passenger floorboard at the point where the firewall meets the floor. Pull back the carpet, and remove the black shield that covers the stuff back there. There are two 10mm-head nuts at the bottom corners - don't lose them down under the carpet (ask how I know).

The large clear line coming from the PSE pump hooks to the P- port on the pump and to port 6 on the distribution block.

To test the block, remove all the connections (pay attention to where the came from) and hook a vacuum tester to port 6. Plug connections 5 & 13. Use a mity-vac tool to evacuate the air. Pump out as much air as you can. The block specs are no more than 25mbar in 1 minute when evacuated to 300mbar. Basically, if you see any movement on the gauge, the block is probably worn out.

The block is connected to the reservoir under the right-front fender behind the tire. There's no check valve in the reservoir, it's in the block. The reservoirs rarely fail, they're in a pretty protected environment. You can get at it by partially removing the inner fender, but I'll hazard a guess that the distribution block is your problem.

The codes on the pump are in German, these are the English equivalents:
ZV = CL Central Locking
RH = BA Backup Assist
FKS = RHR Rear Headrest Release
SFG = RTG Retractable Trunk Lid Grip
PU/P+ (OSL) = PU/P+ (OSB) Lumbar supports
PU/P- (SRU) = PU/P- (MVA) Manifold Vacuum Assist - this is the circuit you're interested in.

OK, I will check that out, and I'll post my findings. Thanks!

I did see that block, I bypassed the block by taking the vacuum feed into the block and connecting it directly to the switchover valve, and i get the same results. I wasn't able to find anything on alldata about what the other lines connected to the distribution block. Even with me bypassing the distribution block and getting the same results, do you still think it is the block?

The check valve manifold/ distributor part number is 129-800-14-78. MB $40 list

The only real way to find the problem is with a vacuum pump and guage, see what leaks & then block off that leak & see if the problem goes away.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Since I don't have a might vac, I decided to check the reservoir first and both lines into the reservoir had been broken off or cut. I'm in the process of reconnecting them now. I can't find the other part of the line (that feeds into the cabin, so I'm connecting them in at the manifold directly. I think the previous owner had messed with the vacuum lines trying to fix the problem. Do you know the correct color vac lines that correspond to the #'s on the switchover valve?

Is that part for 1996 s320? I went down to Mercedes ( I forgot to bring the #) and they could find a part under that name. The guy quoted my over $500.00. I told him that was probally the switchover valve. About the distributor, when I look on alldata it lists port 5 & 13 that need to be connected, however I only have 1-6 ports, is there something I'm missing? Plus it lists the lines coming from the reservoir to be red-green and gray-green, but I don't have those color. Do I have the wrong picture?

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Ok, here's what I have so far. I figured out the correct vac lines for the switchover valve. I bought I vac and tested the manifold (although I couldn't use the info you provided me because I don't have a # 13 on the manifold). I tested using the P port (which had no stopper) I found that it was indeed leaking at a pretty fast rate. It's weird, I thought I would hear something. I'm going to try and buy the manifold tomorrow and I'll let you know if it works. Just out of curiosity, how does the PSE pump help the manifold. I'm thinking that the vacuum from the manifold is received at the PSE, from here I'm lost. How would the PSE transfer vacuum to either the reservoir the manifold?

Thanks to MB Doc and Wbrain63! I installed the new manifold and it works great, even under heavy acceleration!