Hello All -

I was driving the SDL on the expressway yesterday with the economy vent on when all of a sudden it switched to the defroster vents all by itself. Now the only place she will blow air from is these vents. In trying to figure out what's going on I also noticed that the compressor will not engage. Fuses under the hood are all o.k. Any ideas/suggestions for trouble shooting would be greatly appreciated .

Thanks,

Keith

Check the red/gray (I think, don't remember the colors on the W126) vacuum line in the engine compartment next to the brake booster. Sounds like the vacuum supply is gone, so it will default to defrost only. If the temp control is fine, this is the problem. If it get hotter than all getout, you have no electrical power to the pushbutton unit.

This should not, however, kill the compressor -- check for a bad serpentine belt as the Klima will shut it off if the compressor slows down for any reason.

Also, replace the fuse, they can be cracked and still look fine. Don't know off the top of my head which one it is on the W126, but it's on the cover panel.

Note that on this particular application (OM603 engine), a blown EGR or air recirc actuator (pretty common at this age) will drop the vac available to the ACC below what it needs to work, so check that all four branches of the 5-way T at the front of the engine hold vac. Mine are both blown, I just plugged the T.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

It didn't seem to get any hotter so hopefully I can figure it out in the morning. Thanks a million!

Keith

I replaced the fuse and it didn't make a difference. I checked all of the vacuum lines I could locate (visual and manual inspection) and didn't notice any cracks or problems. The compressor will still not engage but the air coming into the cabin is not super heated. On a test drive I found that the center dash vents started to work at speeds above 10 mph or so. I thought it might be the air pressure from the plenium but I even heard a "click" once and they stayed on for almost 20 minutes worth of cruising, even at stoplights. Now the end mid level vents are working but not the center ones. Any suggestions would be greatly appreciated.

Thanks,

Keith

'87 300 SDL 220,000+

I'm with Peter, sounds like vacuum. You will need to use a vacuum gage, though, since the EGR and air recirc diaphragms that could be leaking are not visible.

More reinforcement for the vacuum leak theory. More rpm means more vacuum pump rpm which can 'suck' more air out of a leaking system, allowing the vent controls to operate.

The end vents on my SDL blow air whether the defrost or center vents are open. I believe they are fixed ON, as 'leak air' vents unless you manually close them.

If you don't have a vacuum gage, locate the EGR and air valve lines and plug them, at least temporarily, and see if it helps.

Best Regards,
Jim

Can anyone tell me if the Air Recirc. Actuator is located in the dash? I went to lunch in the SDL today and heard a wierd, high-pitched and raspy squeeling sound coming from what sounded like behind the glove compartment area. It has never done made this noise before and it lasted for about a minute after I started the car. Possible vacuum problem?

As usual thanks to all!

Keith

PM me with your email and I will send you the complete diagram.

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I have personal experience with this exact noise.

There is an aspirator motor that draws cabin air into the climate control system. This motor has run all the time for the last 20 years and it is time to give it a cleaning and a drop or two of oil.

Remove the underdash panel from the passenger side and the motor will be just above it. It's not very large and it has a hose attached to one side, IIRC. Take the motor and housing out and thorougly clean the journals. Put a couple of drops of oil on them and put it all back together.

Noise gone.

the air recirc valve is on the turbocharger, completely unrelated to the ACC except for the vacuum supply system.

You have a vac leak, either in the engine compartment or the dash. This is unrelated to the compressor not running -- either you are low on charge (find the leak!) or the belt is slipping.

The air recirc valve and EGR valve acutators are behind the air filter box, sort of below it. I think you can reach them easily on the SDL, on the W124 they are buried.

You need to get a MitiVac hand pump, it's very difficult to check things out without one. Attach to the lines at the 5-way T connector at the front of the engine -- the two branches on the right (passenger) side go to the EGR and air recirc actuators, the left side to the ACC and the transmission shift controls. Check each in turn, they all must hold vac except the tranny one, it will leak down slowly.

New actuators were about $60 last time I looked, probably more now.

Check the condition of the hoses and rubber fittings, expecially the small yellow plastic "connector" under the 5-way T. It is actually a restriction, and may have gotten plugged.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Thanks to all who have helped so far. I'll be buying a Mity Vac tomorrow and hopefully putting it to good use on Saturday.

Keith

No need to replace the actuators when all you need is the rubber diaphram inside.

Buy them here: http://www.autoluxmbz.com/

Second item down.

I've replaced a number of them in my SD's.

__________________
Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)

How critical is that yellow "connector/restrictor"?

I removed mine after changing the vacuum pump and replacing much of the vacuum hose connections. I thought at first it was a one way 'check-valve' but it seemed to allow air flow in both directions, so I just used a solid piece of hose there.

I don't have any noticable vacuum problems, although the Tranny can be a little harsh shifting at low speeds sometimes, smooth as silk at others.

__________________
1991 M-B 560SEL Arctic White/Grey 99,000 Miles
1987 M-B 300SDL Ivory/Palomino 229,000 Miles (sold but never forgotten)
2006 Volvo XC70 Blue/Beige
1999 Porsche Boxster Arena Red/Savanna Beige
1986 Porsche 928S Goldweiss/Brown