The main air / recirc flap position is not directly related to the EC button. It also depends on interior air temp, exterior air temp, and the desired temp selected on the controller wheel. What is shown in that video is likely correct for the conditions when that video was taken. Your car may not do the same thing since your conditions won't be identical.

You need to read the factory climate control manual and verify all your plumbing is correct, then follow the diagrams and see if it's working per factory specs. Link below, see section E, PDF pages 9-13 of 35.

http://www.w124-zone.com/downloads/MB%20CD/W124/w124CD1/Program/Climate/83-600.pdf#page=9

Pressing the recirculation switch (S24) SHOULD provide vacuum to both ports of both flaps, and fully close the main air flap.

Great intel.
Thanks for taking the time ....

I took apart the dash in my 1987 300TD and replaced two vacuum pods with NOS units and rebuilt the others with the kit sold by Performance Analysis. I also replaced all of the little rubber connectors. Using my Mity-Vac, I'm able to draw vacuum at the glovebox manifold, firewall, and five-way tee in the engine compartment (with the Mity-Vac pointing towards the passenger compartment). However, with the electricity on or with the car running, the HVAC control buttons do nothing to change the direction of the air. The defroster flaps are open all the way and the center flap refuses to open. Swapping out the panel with the control buttons did nothing to help.

Any thoughts?

Many thanks,

Corvo Gold
1987 300TD, converted to manual shift

Did you also test each of the 7 vacuum lines to each vacuum pod, and confirm all 7 hold vacuum? That will confirm your repairs were successful.

Next test is with the engine running, check for vacuum at the inlet of the 7-port manifold. If there is no vacuum present, you need to work backwards towards the engine vacuum pump and find out why.

If there is vacuum present at the 7-port manifold with the engine running (should be ~25" Hg), and NONE of the pods move when different modes are selected, you may have an electrical issue, or faulty pushbutton unit. With max cool ("EC" mode), the center vent should open, the footwell flaps should close, and the defrost flaps should close. With max cool and recirc switch pressed, the main air (recirc) flap should close.

Climate control FSM documents are at the link below if you don't have them:
83 Climate Control System

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Dave
Boise, ID
Check out my website photos, documents, and movies!

GSXR,

Thanks for the response. Now that I'm back in town I can commence to wrenching.

My vacuum pods are all good. Two of the dual-chamber pods have a very, very slow vacuum leak because on each pod one of the four tabs that holds the assembly together snapped off. I'm finagling two replacements, so it should be rectified shortly.

I get about 3" Hg at the manifold input. When I plug off all of the lines at the five-way connector in the engine compartment, save for the line to the vacuum pump and the line to the HVAC, pressure at the manifold input jumps to 22" Hg. However, pushing the buttons on the control panel still does nothing. This leads me to believe I have both an electrical issue and a vacuum issue.

The five-way connector is new as of today and I replaced whatever else I could with universal vacuum hose. I plugged the lines that went to the auto trans that's no longer there. I'm going to have to order some of the more unique rubber tees in the engine compartment.

My blower motor does not maintain a steady speed on high, which leads me to believe the regulator is bad. Would this effect the HVAC blender door buttons?

Thoughts?

Many thanks,

Corvo Gold
1987 300TD, converted to manual shift

±22" Hg is normal and correct. You have a vacuum leak somewhere in the engine compartment to locate and repair, but for now you can bypass it and get full vacuum to the 7-port manifold for HVAC testing.

You may indeed have an electrical issue also. The 7-port manifold is a pretty rare failure, but the HVAC control unit is known to be problematic. Also verify the monovalve and auxiliary heater pump are not shorted (or low resistance, pulling more current than normal).

The blower is a separate issue, and if the fan speed varies with the high-speed button pressed, something weird is going on. It's not necessarily the regulator. A failed regulator generally results in either no fan at all, a fixed speed, or only variable between low and medium. The pushbutton unit sends a speed signal to the regulator, so if the control unit is sending a faulty signal, that could result in the odd fan speeds. Search the forum for more details on this, and/or the 500E board forum.

If you have a spare pushbutton unit, swap it out and see what happens.

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Dave
Boise, ID
Check out my website photos, documents, and movies!

I do have some spare control panels — an embarrassment of riches, in fact. I swapped one in and no change, but I can swap in the others to further confirm.

I’m attempting to scare up another vacuum manifold.

Question regarding the dual-chamber actuators: are the assemblies all the same with different length actuating rods? That is, if I had a line an NOS example of one, can I swap out the rod and use it elsewhere?

Many thanks,

Corvo Gold
1987 300TD, converted to manual shift

If a different control panel resulted in no change, hmm... I'd unplug the aux pump and monovalve for grins. These can cause the control unit to enter a sort of 'safety mode' where things don't work right. Easy test, and free. I doubt the 7-port manifold is bad but if you can swap that, go for it.

The dual-chamber pods should be mostly the same, with different metal rods. You may need to re-clock the housing so the mounting ears and vacuum ports are aligned correctly. But yes, if you can find another one, it should be useable. Has to be from a 124 chassis though, IIRC other chassis (i.e., 126) use physically different pod sizes. (??)

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Dave
Boise, ID
Check out my website photos, documents, and movies!

GSXR,

Where oh where is the aux water pump located in a 1987 diesel wagon? Past threads say under the washer fluid reservoir, but perhaps that's true in a gas powered car.

Here's the latest:

- All pods hold good vacuum

- I've swapped in four different push button control units. Switching the unit on or off moves the dual-chambered pods, but that's it. None of the other buttons have any effect.

- I installed a band-new vacuum control valve (seven-port manifold) for a W126 -- it's reasonably inexpensive and the only difference is the housing. No change.

- I unplugged the mono valve. No change.

- Can't locate the aux water pump!

Question: what is the source of the 8-wire plug that fits into the seven-port manifold?

I appreciate any insight.

Many thanks,

Corvo Gold
1987 300TD, converted to manual shift

The aux water pump is located below the washer fluid reservoir on the diesels. Follow the heater hoses in that area. If the pump is missing, someone may have bypassed it. Normally the hose routes from the firewall, to the pump below the reservoir, and back up to the pipe at the intake manifold near the throttle cable area.

The wiring to the 7-port manifold comes from the pushbutton control unit, which controls the manifold, telling it which vacuum ports to open or close.

If the pushbutton unit moves the dual-chambered pods, it's doing SOMETHING. Remember the other functions (opening single-chambered pods) depends on both the buttons pressed, temperature selected on the wheel, AND cabin temperature from the sensor in the dome light assembly. If you set the desired temp to max cold (click the detent on the wheel) this should open the center vent pod.

You'll have to start going through the factory manual which describes operation in various scenarios. Here's a link:

Attached Thumbnails

 

Well, that's interesting: my hoses look nothing like that. There's just one hose running from the firewall into the intake. What's more, since I've owned the car there's been a two-pronged plug that isn't plugged into anything.

Well, dog my cats....

Why would someone remove the aux water pump? Will reinstalling it perhaps make the HVAC work as it should?

I feel like these are incredibly basic questions, so thank you for humoring me.

Corvo Gold
1987 300TD, converted to manual shift.

Someone bypassed / deleted the aux pump on your car. You'll probably find the electrical connector unplugged below the washer reservoir.

Why would someone do this? To save money. A replacement pump is ~$100 or so, and the only function is to keep the heater from gradually cooling off when sitting at a stoplight in cold weather. The pump is basically useless in warm weather and with engine RPM above idle. It won't fix any of your issues.

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Boise, ID
Check out my website photos, documents, and movies!

I discovered why the pod inside the heater core wasn't opening the door to which it's connected despite holding a vacuum. Turns out, the rank amateur who rebuilt it forgot to reinstall the spring. It now opens when I turn the temp dial all the way to cold.

Nevertheless, I still haven't seen the pod at the top of the heater box operate via the control panel. It holds vacuum all the way down to the manifold.

Corvo Gold
1987 300TD, converted to manual shift

Good to hear you figured out the center vent.

The smaller round pod at the top, for the diverter flap, only opens under certain circumstances. I don't know how to "force" it to open with a combination of buttons and temperature selection. If everything else is working, and the diverter flap opens when you apply vacuum manually, you should be fine.

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Boise, ID
Check out my website photos, documents, and movies!

Update: All of my vacuum pods are working like they should. An independent shop blessed my work and got my a/c going again. I put the dash back together this past weekend.

So what did I learn? This is going to seem so painfully obvious, but the temperature dial controls the pods just like the buttons do. What's more, the center vent does not blow hot air; it opens only for the a/c. Also, the button with the outline of an arrow pointing up is what gives you a/c (not the one that says "EC").

I also learned that not all control panels are the same. My '87 diesel quite possibly uses a different control panel than its gas-powered brethren, but happily I had one in my parts stash. Unfortunately, the two light bulbs that illuminate the HVAC buttons aren't coming on even after replacing the bulbs. I stuck a test light in the bulb socket, but it didn't illuminate.

Corvo Gold
1987 300TD, converted to manual shift