Quick Troubleshooting tips needed for floor vents - PeachParts Mercedes-Benz Forum

ck42 · #1 01-25-2003, 03:06 PM

Looks like neither of the floor vents are working.

From a quick search, I've not found very much info on these bottom vents.

Can someone give me the primary areas of operation that can be suspect when the floor vents aren't operating?

About all I know right now is that there are switches inside the dash that receive an electrical signal which then sends a signal to the vacuum switch which operates the flap on the vent.....is this correct?

Any tips would be most appreciated.
car is an '85 300SD

psfred · #2 01-25-2003, 03:15 PM

Chris:

Let me guess:

You only have defrost, no floor heat no matter what button you push on the climate control, right?

Do you have blower control, or does it run at low speed only?

Low vac will cause the system to run in only defrost. If the fuse is good, you will have temp control, but no air flow anywhere but the dash.

If the fuse is blown, you get full heat, defrost only, at a fixed blower speed.

A bad connection in the green vac line or a plugged orifice will cause the system to run only defrost.

ck42 · #3 01-25-2003, 03:29 PM

Actually, I think everything is working perfectly.....except no floor heat.

Blower control works fine.
Heat comes out top and side vents fine.
A/C works fine too.

On a side note:
I just noticed on the vacuum schematic that the floor vent switchover valve is the only valve that has an "Orifice" attached to its output. Why?

Chris
'85 300SD

psfred · #4 01-25-2003, 03:44 PM

Chris:

Servo is shot then, most likely. Or a hose is off the switchover valve.

The orifice is to allow partial servo position, I think. Slows the diaphram action down. I think this servo is a dual diaphram, too, but I could be wrong.

Peter

ck42 · #5 01-25-2003, 03:51 PM

Ok....so:

The switchover valve is not receiving the electrical signal

OR

the switchover valve OR the servo is not functioning

OR

there's a vacuum issue with either the switchover valve or the servo.

Should these scenarios take care of 95% of possible issues?

Chris
'85 300SD

engatwork · #6 01-25-2003, 03:56 PM

Chris - cheap, easy fix if you don't want to mess with the servo right now. Remove your drivers side "side" (the one under the dash, drivers side, behind the radio) panel and tie wrap the diaphragm that opens the floor vacuum damper actuator in the open position. If you want to get into the troubleshooting now (with the panel removed) is the time to do it. Put your mighty vac on the actuator and see if it opens/closes. Also, put it on the vacuum system line to see if the vacuum signal changes as you mash the different buttons on the climate control. If it were mine I would just tie wrap it open for the time being. You can go back in there around March and remove the tie wrap.

ck42 · #7 01-25-2003, 04:00 PM

Enga....ja, I'll prolly just 'rig' that flap open for the time being.

When the temps around here warm up a bit more, I'll do the actual t/s'ing.

I just wanted to get an idea of what items I would be t/s'ing when I dug into the dash.

Thanks guys!

Chris
'85 300SD

engatwork · #8 01-25-2003, 04:06 PM

Chris - my experience is worse case $$ you would have to replace the pushbutton unit. Otherwise (assuming no vacuum line/diaphragm leakage issues) is replacement of the vacuum switchover solenoid that are pretty much directly behind the pushbutton unit. I have replaced all five of them in the 300D along with the pushbutton unit (now all I need to do is get the engine/tranny back in it

after it starts getting above 55 dF during the day on weekends). The solenoids are straight forward but more of a pia than anything else because they are in a pretty small space. All of this is diy'er work

.

ck42 · #9 01-25-2003, 08:33 PM

One last question here..... I promise

I looked up under the dash and there's the black plastic shield that covers the entire area above the pedals.

Do I need to remove this piece in order to gain access to the floor vent flap? ...and where *is* the flap? close to the tranny tunnel or by the door?

Chris
'85 300SD

engatwork · #10 01-25-2003, 08:44 PM

I'm not exactly sure about the SD model but if I remember correctly on the 300D the kickpanel above the drivers footwell does have to come out to remove the side panel on the tranny tunnel. Again on the 300D the actuator you are trying to get to would be to the right of your right foot (as you are seated in the drivers seat) about 6-8" off the floor (behind the right hand panel). I suspect the actuator in the SD is in pretty much the same place.

MVK · #11 01-25-2003, 10:15 PM

Hi Chris:
I agree with engatwork on the space limitation during changing of those 5 valves. I did one of them. I posted the pictures on the forum in May/June 2002. search under my name MVK and key words like switch over valves and you will find them there.
OK here it is

Defrost Vent always open- How I fixed it.

They are pretty detailed photos. NOW MIND YOU THOSE ARE FOR 1985 300D TURBO. I am not sure how diff it is from yours.
Yes on my car I had to remove the whole kick panel. Dont forget that 2 or 3 screws on kick panel are hidden behinf little plastic cover tabs. Not too difficult to get it out. Also once you take the panel out, you might find a black vac tube with open end. and you will think you knocked it out from somewhere. I went cookoo looking for where it fits. LOL

I hope the photos will help you.

MVK

ck42 · #12 01-25-2003, 10:55 PM

Enga and MVK,

thnx again. MVK, that thread is perfect. The pix, if accurate for the SD, show me exactly where to look.

mvk...regarding the black hose tho, *does* it go somewhere? ....or was it not suppose to connect to anything in your case? you never said LOL

Chris
'85 300SD

engatwork · #13 01-26-2003, 08:07 AM

Chris - I think MVK is referring to the vent hose that comes from the engine compartment (originates from the side of the tranny vacuum controller located at the back of the fi pump).

MVK · #14 01-26-2003, 10:35 AM

Hi Chris;
Yes that black vent stays there and is not attached to anywhere. It sucks clean air for the system. The reason they put it in the cabin and near the steering column is that its one of the least disturbed and cleanest area in the car. This way the suction will take in only clean air( unlike engine compartment which is dirty and dusty).
I hope the photos help you. I might have more if you want send me your e-mail.

MVK

ck42 · #15 01-26-2003, 12:56 PM

Ok...thnx for clearing that one up

One last thing....I've noticed that there is no heat coming from EITHER side of the footwells.
On the schematic, there doesn't appear to be a Left and Right side.....are there vents on both sides?

If so, then the likelyhood that both have failed seems low...

Chris
'85 300SD