1987 560sl dash vents always open and blow hot air - PeachParts Mercedes-Benz Forum

dialric · #1 06-25-2009, 12:02 AM

I just purchased the car. The compressor belt has been removed by last owner. All of the dash vents are open, and stay open. when i push the heat buttons nothing changes. I get hot air from all my vents. I moved the wheel up and down to see if any chage would occur. Nothing happened. Can somebody please tell me what to look for. I did repaced the monovalve and before I replaced it I did not have hot air blowing out of my vents. thanks richard

Jim Anderson · #2 06-25-2009, 01:12 AM

In a Mercedes all heat (and defrost) all the time means no vacuum. It's the default position for all the vacuum actuators and doors.

dialric · #3 06-25-2009, 04:14 PM

Jim, what do you mean by default position.? Does the vacuum to the dash vents come from behind the glovebox?

Philip J · #4 06-25-2009, 07:11 PM

Yea,mine does the same, have tried to correct it but have had no luck, also did mono valve. Philip 87 560 sl 45k

Walrus · #5 06-25-2009, 09:06 PM

Quote:

Originally Posted by Jim Anderson

In a Mercedes all heat (and defrost) all the time means no vacuum. It's the default position for all the vacuum actuators and doors.

I don't accept this postulate. Navigate to www.rmsmithco.com and click on the link to 107 center vent information.

Several causes are possible, with a broken heater box mounting very likely.

dialric · #6 06-27-2009, 02:52 PM

OK, before i start checking for leaks, can someone tell me where i can purchase the parts. I am still a little mixed up as where to start. thank you Richard

dialric · #7 06-27-2009, 11:03 PM

I pulled the glovebox and checked the vacuum at the switchover valve line from manifold showed and held vacuum. Switch # 1 showed and held vacuum. # 2, 3 and # 4 showed o vacuum on the guage. i checked pod 43 and it held vacuum. Where do I go next ? thank you

Walrus · #8 06-28-2009, 12:30 AM

Quote:

Originally Posted by dialric

I pulled the glovebox and checked the vacuum at the switchover valve line from manifold showed and held vacuum. Switch # 1 showed and held vacuum. # 2, 3 and # 4 showed o vacuum on the gauge. i checked pod 43 and it held vacuum. Where do I go next ? thank you

Refer to the test procedure I wrote in my website, along with the vacuum circuit I posted there.

I am going to dangerously assume no one has buggered up your system, and all is still connected as the factory intended. I am also gonna assume a '87 560 is the same as a '88 560 (I'm not gonna take the time to research).
Go back to the diagram I posted and then describe how you checked pods (there are two per fresh air vent) 43... The line to switchover valve #4 goes thru the S24 recirc switch, then to pods 43 and pods 42. If the vacuum pump/gauge was attached to the vacuum line that was attached to switchover #4 did not hold vacuum, Leaks could be in hose connections, at S-24, or any one pod. You will need to separate the two pod circuits and check each circuit, and then each pod. If one or more are leaking, then just plug the switchover valve #4 with a rubber hose and golf tee. If all other circuits check out, then the leak in the recirc circuit may be enough to prevent other circuits from functioning. Since you report 2, 3 and 4 did not hold vacuum, I doubt a leak in the recirc circuit is the problem. It is a problem, but a leak here does not affect the other circuits attached to #2, #3, and #4.

I don't expect you to have much success in the long term. If one diaphragm is ruptured in one pod, then likely you'll have others.

If you disconnect the vacuum lines from switchover valves number 2 and 3, and your center vents still stay open, then expect a broken heater box where the pod mounts. Without vacuum, the center vents default to closed (a spring in the pod pushes the vent closed). If the pod mounting is broken loose, the pod can't push anything. A quick test is to take a pencil and reach thru the center vents and gently push open the vent. If it is already open, or stays open when gently pushed, your pod is broken loose in all likelyhood (see text of website).

If you apply vacuum to the line that was attached to switchover #2, and it holds, then 1/2 of pod 38 and 40a are good. if the line won't hold vacuum, then you'll need to check each separately. This aint fun...

If you attach the vacuum pump to the line that was on switchover valve #3, and it holds vacuum, then the long throw of pod 38 is good. If it will not hold vacuum, then like above, you got problems.

If it is any consolation, having line #1 hold vacuum means the pod that works the vents at your feet is good... for now.

I suspect the following: Diaphragms in pod 38 (one or both) are fubar. Heater box is broken out where pod 40a mounts (see pictures on website). One or more diaphragms in pods 42 and 43 are fubar. Incidentally, pods 42 and 43 are identical, and all diaphragms, except for the short throw in pod 38, are the same, IIRC.

If any of the above is the case, you gotta determine how much you want the system to work. The fix aint gonna be fast or easy. If you choose to go the dealer or mechanic route, expect $1k or better in labor and 1-3C notes in parts (diaphragms are cheap, but pods are kinda pricey, if the housings break during dis-assembly).

dialric · #9 06-28-2009, 09:15 AM

Where can i purchase the pods and the diaphrams? and thanks for leading me in the right direction.

Walrus · #10 06-28-2009, 07:35 PM

Quote:

Originally Posted by dialric

Where can i purchase the pods and the diaphragms? and thanks for leading me in the right direction.

Numerous places, but you'll have to call. I don't think the parts are listed on the on-line catalogs. Start with Fastlane, the owner/operator of this site.
Don't forget the dealerships...

If you navigate to Fastlane from the link at the top of this forum, you can drill down to your '87 560SL. There you can type in a search word "vacuum" and all sorts of info will be available to you.

dialric · #11 06-28-2009, 11:06 PM

Walrus, I noticed that the fan will only blow when the defroster button is depressed. when i depress all of the other buttons, nothing button on the far left fan on and the 1 one the far right Do i have a defective panel ?

dialric · #12 06-28-2009, 11:11 PM

please tell me where S24 rec. switch is located

dialric · #13 06-29-2009, 05:29 PM

Walrus, I call my local Benz dealer. Parts person told me that he shows 6 pods,I told him that there were 7. He asked me if I had the part #s. He checked by using the VIN of my car. Help please

Walrus · #14 06-29-2009, 08:58 PM

Quote:

Originally Posted by dialric

please tell me where S24 rec. switch is located

Right here

Walrus · #15 06-29-2009, 09:02 PM

Quote:

Originally Posted by dialric

Walrus, I call my local Benz dealer. Parts person told me that he shows 6 pods,I told him that there were 7. He asked me if I had the part #s. He checked by using the VIN of my car. Help please

On the '88...
2 on left side of the dash (fresh air inlets)
2 on right side of the dash (fresh air inlets)
1 in the lower heater box (foot vents)
1 in the upper heater box (center vents)
1 to the left of center outside the heater box (combo 2-stage valve for defroster vents)

I am not aware of the '87 being any different...

Show him the following diagram...