My 85 300D heating system seems to be working just fine except that the leg vents never open up. Fresh air, warm air, and hot air seem to be coming out of the side, center, and defrost vents at the appropriate times. I have the M-B manual on CD-rom, and it points to the "switchover valves", a horizontal row of five devices -- one of which is supposed to activate the vacuum element that opens/shuts the leg vents, but I have not been able to locate them. Could someone please direct me to their location?


Thanks,
Dan

Dan:

The switch over valves are located behind the panel where your AC climate controls that you operate are located (M-B calls the AC controls the control panel and gently prying the panel off that surrounds the control panel and removing the temperature selector/control switch assembly will reveal the switch over valves - you will probably need to remove the ash tray and the radio to have enough room to get the panel off around the control switch off). I and other members recently wrote about working on these systems. However, that problem was with cold air not coming out of the center vents - the comments, suggestions, and opinions in that post also apply to the problem you're having. Look up that post for help.

Good Luck!
Tom

__________________
America: Land of the Free!

1977 300D: 300,000+ miles

American Honda: Factory Trained Technician & Honor Grad.
Formerly:
Shop Foreman;
Technical Advisor to Am. Honda;
Supervisor of Maintenance largest tree care co. in US for offices in Tex.

I did take the control panel, ashtray, and radio out the other day, but I couldn't find anything that looked like the switchover valves that were pictured in the CD-rom manual. I'll try to look up the previous thread on this topic. I had already done a search but didn't come up with anything for my specific problem, but I'll check again.

Thanks for your help,
Dan

Do a search for a thread started by Gary F. entitled center AC vents not working (or close to those words) dated 3-21-02. GSXR wrote that on his '85 300D the switchover valves are located where I described them - behind the control panel (the device with the push buttons to control fan speed and temp). When looking for info about the AC system, you should be more concerned about general info because the various sub-systems (the valves, actuator, switchover valves, lines, etc., etc.) generally work the same way, it is where the sub-system components are located and accessed that is the particular problem you have but may be fixed by another member's way to fix their particular sub-system. Am I making sense to you?

M-B is bad about not showing where components are located in the "official" service manuals. The M-B dealership techs get that info in service bulletins not available to the public (trade secrets).

Good Luck!
Tom

__________________
America: Land of the Free!

1977 300D: 300,000+ miles

American Honda: Factory Trained Technician & Honor Grad.
Formerly:
Shop Foreman;
Technical Advisor to Am. Honda;
Supervisor of Maintenance largest tree care co. in US for offices in Tex.

In my 300D they are behind the pushbutton panel. There should be five of them. There should be a couple vacuum hose connections and wiring to each valve. I have had to replace 3 since purchasing the 300D.

__________________
Jim

Tom,
I found the Gary F. thread and the switchover valves, all conveniently numbered 1 thru 5. An interesting thing is that in doing the search for information on my specific problem, I have not gotten any hits on leg vent problems -- plenty on center, side, and defrost vents though. Maybe this indicates that the leg vent design was better than the other vents. That or people just don't get worked up over lack of heat around the feet.

Dan

Dan:

Congrats on finding the switchover valves. Yours are numbered! Mine are not, plus I have to remove the driver's seat and the entire console to access the switchover valves and other AC components located there - you guys with the later W123's have it relatively easy to work on that part of the AC system. Can't say why the floor vent sub-system seems to not have problems like the other AC sub-systems have - the components are all the same (switchover valves, actuators, vacuum lines, etc., etc.). You may be right about others not complaining about the lack of floor heat and, thus, never posted a thread. Personally, I don't like cold feet and would fix a problem with the floor vent sub-system if it was not working.

Let us know what your problem is so others can fix their AC floor vent sub-system if they have the same problem - especialy since your problem seems to be unique.

Good Luck!
Tom

__________________
America: Land of the Free!

1977 300D: 300,000+ miles

American Honda: Factory Trained Technician & Honor Grad.
Formerly:
Shop Foreman;
Technical Advisor to Am. Honda;
Supervisor of Maintenance largest tree care co. in US for offices in Tex.

Tom,
I was able to get better access to the switchover valves by popping out the horizontal row of rocker switches above the ACC panel and removing that panel as well. Though I was not quite ready to remove the potentially offending switchover valve today, and not yet having the proper vacuum testing instrument, I was limited in my troubleshooting to pulling the vacuum output hose off the switch and seeing if I could feel any vacuum effect with my thumb over the vacuum-out spigot of the switch whilst running the ACC through its paces. I felt no such effect whatsoever, so my inclination is to think that the switchover valve either is not working or is not getting the proper signal to activate. What is this Mity-vac that I have seen mentioned? Is it something that a DIYer can pickup at an autoparts/tool store, do you know? I think I would like to apply vacuum to the leg flap actuator to see if that mechanism is working properly before I delve into the switchover valve itself. I have to assume that the vacuum circuit before it gets to the switchover valves is working fine because the other vents seem to work properly.

Dan

Dan:

Sounds like you've made good progress. You're right, you need the Mighty Vac to check the various components to see if they work or not, plus find leaks. After replacing a bad actuator I still had vacuum leaks and tracing/testing the lines found a 2" long vacuum line that leaked and a Y plastic fitting that also leaked.

I bought my Mighty Vac years ago from NAPA. I've also seen them at O'Reilly for about $30. Call around to local auto parts suppliers to find one where you live. There are online tool suppliers that have them, but finding one locally will save time and $. If you can't find one locally let me know and I'll let you know of at least one place where you can buy it. The Mighty Vac can also bleed the brake lines/master cylinder, draw fluid from hard to reach places, and other procedures - so its a useful tool for later maintenance/repair operations.

Tom

__________________
America: Land of the Free!

1977 300D: 300,000+ miles

American Honda: Factory Trained Technician & Honor Grad.
Formerly:
Shop Foreman;
Technical Advisor to Am. Honda;
Supervisor of Maintenance largest tree care co. in US for offices in Tex.

Tom,
In the "it's always something department", I located a MityVac at a PepBoys about 20 miles from me ($40.), but this morning when I had a chance to get it out and perhaps start my diagnosing labors, I notice that a screw is missing from the cap on the piston chamber. Sheesh! How does anything ever get done in this world?

Dan

Dan:

Yep seen the same movie (or rather nightmare!) too many times. Is the Migthy Vac the plastic or metal version? Mine is the metal version and I put a bit of grease on the pivot/contact points - made it work a lot easier and last longer since the metal won't grate. If you have the plastic version, I would still think a bit of grease on the pivot/contact points so it will work easier and last longer.

Tom

__________________
America: Land of the Free!

1977 300D: 300,000+ miles

American Honda: Factory Trained Technician & Honor Grad.
Formerly:
Shop Foreman;
Technical Advisor to Am. Honda;
Supervisor of Maintenance largest tree care co. in US for offices in Tex.

Dan,

I think that I had the same problem with the leg vents not having air pushed through them.

At least on my configuration of leaks, I was able to get air to come out of the leg vents pushing the second and the fourth buttons on the ac selector. The ac trouble shooting manual describes what is supposed to happen if you push multiple buttons at the same time, and then goes on to say that you shouldn't do it "on priniciple", but that it won't hurt anything.

At least I have warm feet until I can take apart the consol and trace the leaks.

later

__________________
84 300TD - 235k - Farbe "Surfblau" bought at 213k
87 300SDL - 131k - Farbe "PimpGold" bought at 115k
00 Klepper Faltboot Expedition Double

Thank, I"ll check out your multiple button trick as soon as it cools down a bit. Right now we're having a record heat wave with 90 degrees plus, and guess what?...my AC isn't working. So that has priority at the moment.

Dan

Then I looked and there was no belt on it.

The things that you learn when buying a new car with no prior mechanical knowledge.

Hopefully, you can fix yours as easily (~$10 for a new belt).

good luck

__________________
84 300TD - 235k - Farbe "Surfblau" bought at 213k
87 300SDL - 131k - Farbe "PimpGold" bought at 115k
00 Klepper Faltboot Expedition Double