lowsy heater 86 SDL - PeachParts Mercedes-Benz Forum

AlanTbird · #1 12-02-2006, 01:17 PM

so its getting cold here in AZ
believve it or not...it was mid 30 this am

My SDL has little or no heat!
I have searched the archives and after messing whith my pump and monovalve i find this:
the valve clunks when I put 12v to it and the motor wirrs when I do the same.
It seems theres no ground to the valve so i attached a wire that when the car is calling for heat I get a spark on the ground wire to earth.

Weird cause i read that the valve defaults to OPEN. and only gets 12v when needing to shut off?

Could there be a flap in the cabin thats not moving?
everything else seems to function right...the vent to the floor is open when its calling for heat and everytyhing else seems proper but still get luke warm air at the most!

I even 1/2 blocked the radiator with cardboard yesterday (OLD PA. TRICK) to get the eng temp above 80 with no results!

I really am trying NOT to remove the valve and pump cause it looks like a 4letter job! @#$% LOL!

any advise would be GREATLY appreciated.

kerry · #2 12-02-2006, 01:30 PM

Try disconnecting 12v from the monovalve and see if you get heat.

SD Blue · #3 12-02-2006, 01:42 PM

Hmmm.......Fresh/Recirc Flap???
I'm not sure if yours still has this, but in the glove box there is an oval plastic plug. Try removing it and with a good flashlight you should be able to see the fresh/recirculating flap move with different ACC selections.

I believe replacement of that vacuum pod runs about $50. (Note: I believe Brian Carlton mentioned that the replacement diaphragms from autoluxmbz won't work for the long-throw pods, ie...defrost & recirc.)

Jeremy5848 · #4 12-02-2006, 01:42 PM

Yes, the monovalve is supposed to default to "open." This is a "limp home" feature that is supposed to guaranty warm air for the defrost/defog function. The monovalve is not grounded; its two leads come from the ACC, as I recall. If you can hear the valve 'clunk' then it should be working. Even if the internal rubber parts were damaged, they should leak and let hot water through.

When the engine is warm, can you feel the hoses at the aux pump and monovalve? Are they warm? If so, the parts may be OK. You may have a clogged heater core. I assume the a/c works OK? The vent flaps should not make that much difference -- you would get hot air to the wrong places but at least you'd get hot air somewhere.

Try pressing the Defrost switch (left hand most button). That is supposed to deliver max heat and max fan to the windshield vents and the outer dash vents. If you get air, just not hot air, then the ACC system is not clogged with dust and durt -- but the heater core could be clogged internally with crud and rust. Let's hope not, it is hard to get at.

Jadavis · #5 12-02-2006, 04:22 PM

Do you get heat when driving, but not when stopped? If so the Aux pump is out. When you are driving there is enough flow from the mail engine driven coolant pump to run hot water through the heater core as long as the mono valve is opening.

Do you get heat in the defrost position? My ACC is going bad. Right now the only place is get heat is in the defrost position.

-Jim

mplafleur · #6 12-02-2006, 09:01 PM

Quote:

Originally Posted by Jeremy5848

Yes, the monovalve is supposed to default to "open." This is a "limp home" feature that is supposed to guaranty warm air for the defrost/defog function. The monovalve is not grounded; its two leads come from the ACC, as I recall.

Yes, the monovalve closes when 12 volts is applied, this causes no coolant flow and thus no heat. The signal for the monovalve comes from the temperature control unit, over by the passengers right knee.

AlanTbird · #7 01-28-2007, 06:04 PM

still messin with this thing
the other day I played with the temp dial and at one point I was gettin really hot air out of the defrost and cool air out of the a/c vents at the same time.
can never get HOT out at the floor just barely warm.
Sometimes the A/c vents wont come on at all.
Is the brain to this thing inside the control unit were the buttons live?
Am ready to try another one.

sixto · #8 01-28-2007, 08:36 PM

Quote:

Originally Posted by mplafleur

Yes, the monovalve closes when 12 volts is applied, this causes no coolant flow and thus no heat. The signal for the monovalve comes from the temperature control unit, over by the passengers right knee.

IIRC there is a constant +12V to the monovalve. The CCU controls the monovalve through the ground connector.

Sixto
93 300SD 3.0

SD Blue · #9 01-29-2007, 10:43 AM

From reading your original post, I see you mentioned attaching a ground to the monovalve. You will get all kinds of strange scenarios with a constant ground at the monovalve. The ACC controller provides a ground and power, depending on settings. (I went through this on mine when I found that the PO had modified the monovalve wiring.)

Here is what I did to get mine working:
Open the ACC controller and resolder the edge connections where the circuit boards meet in an "H" pattern.
Mightyvac and test the vacuum pods one-by-one. They can all be checked from the vacuum switches behind the kick panel on the RH side of the console. Replace rubber diaphragms in pods that will not hold a vacuum.(www.autoluxmbz.com) or pods in the case of def. or fresh/recirc.
Rebuild monovalve (mine had no heat)
Note: about the only thing I've heard that resulted in taking out the controller is a defective aux. pump. Putting in an in-line fuse, to the pump, remedies that.

Stay away from modifying wiring, do these basics and you probably have an excellent working system.

Modifications and just swapping parts out will be not much more than shooting at rats in a dark barn. You will end up not knowing what does/doesn't work, frustrated, uncomfortable and saying that the climate system is a nightmare.

PaulH · #10 01-30-2007, 11:01 AM

If you get no heat, first just rebuild the monovalve. I've had the "no heat situation" twice in my SDL (126,000 mi.) and each time it was the monovalve. It's easy to work on and there is even a thread that has pictures to follow. There may be another problem, but the monovalve has a reputation for going bad. If you do decide to get an control head, E-mail me and I'll Give you the Web Site where you can get a rebuilt one for, I think, $155. Good Luck.

AlanTbird · #11 02-05-2007, 01:11 PM

ok so I took off the right kick panels to have a look CHEESE AND CRACKERS what a fun job that was! Theres this funny little fan unit on a hose were I thought I would find the temp controller #000 822 0903 but no dice.
can some one tell me were this thing lives?
Also what happened to the web site with repair manuals on it?'mb.braingears?
Is there another one? as I was using that one alot!

SD Blue · #12 02-05-2007, 02:39 PM

I went back and read your original post.............change your thermostat.

BTW, You should not have to block the radiator on these cars for temps in the +30F range. Were talking subzero+ temps where you would need to block a portion of the radiator.

amosfella · #13 02-05-2007, 02:57 PM

What is your car's water temp gauge running at??? I believe the southern cars might have a 55 degree thermostat. I bought a car and an engine from down there, and had the same problem. guage would top out at about 50-55 degrees. changed the thermostat, and life was good. if you need instructions, let me know.

sixto · #14 02-05-2007, 02:58 PM

From 86 the W126 ACC temp controller is integrated into the PBU. The only thing outside the PBU is the blower controller porcupine.

Sixto
93 300SD 3.0

dieselschnell · #15 02-05-2007, 06:19 PM

Hah, the "PA. Method"....I think my great-grandpappy invented it-you'll be pleased to know it's in full effect today here in PA, with temps at about 12 and windy.