HI all
i am having problems with my heat in my 1985 126 380se with about 200000 miles on it, i get nothing but cold air, i replaced the monovalve and it did nothing, i am think i have a stuck thermostat (the engine cools down a little after you start to drive), but before i throw parts at it is there a test to see if its stuck open? i was thinking to start it up and see if i could feel coolant run thru the hose. Also what all controls the heat? my heat is not even luke warm
help its cold here
thanks
kenny

let it warm up and as the engine got hot, the heat went cold ,all with out moving i also took the monovale back out and put it back in, pulled the wood trim and could not see any connections undone on the ccu

Climate Control System Died Suddenly

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84 300SD
85 380SE
83 528e
95 318ic

i unplugged the monovalve last night on the way home and if i did not run the fan warm air would come out of the vents,but if a put the fan on it would get cold real quick any ideas ?it seems like it takes a while for the car to warm up also

I think you have a vaccum problem. I have dealt with this problem for two years on both my 126's without complete success so I am not the guy you want to get advice from.

It seems to me that if your CCU is blowing while the temp wheel is dialed up to warm then the CCU knows the engine temperature. Knowing that leads me to believe that the flap that shuts off fresh air is not closing when the CCU has sent a signal to the vaccum pod that is supposed to close it. It's also possible the pod that's supposed to allow warm air to blow freely through the heater coil isn't functioning properly too. I'd suspect both pods have ruptured diaphragms. Actually, with a car that old I'd be surprised if any of the vaccum pods were still functioning properly.

Perhaps I've said enough wrong about this so as to entice someone who really knows these systems to get involved in your thread.

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84 300SD
85 380SE
83 528e
95 318ic

thanks for the reply, i started to put a new thermostat in yesterday, but a froze bolt and broken radiator drain have me stopped for now. does your heat cool down if you run the cc fan? if i dont run the fan it will seep warm/hot air out of the vents but as soon as i run the fan it turns ice cold

No, my heat does not cool down when the fan comes on.

Stop changing parts. Sometimes that works with ignition and fuel problems but the vent and air system is so foriegn on these cars that they don't make sense until a comprehensive study is done.

I've had two problems with these systems and solved only one of them. The fan wouldn't blow. That was a vaccum problem so I changed every pod except one. That fixed that problem.

The heat wouldn't come out in the footwells. That too seems to be a vaccum problem and it appears to be controled by the vacuum pod behind the CCU panel. The console need to be removed to change or repair this one. I've had no heat in the footwells for years even after complete an almost complete remodeling job.

I've got some time this weekend and I'll help you search for a solution here in the archives of this forum. Whunter has gather and organized a vast and comprehensive library of information on MBs. I have researched topics in this library and found most of what I need there. You should work through this with the understand that as you learn you'll learn how to learn again. You'll develop skills which will help you gleen though topics and remember not particularly where they are but what is most important and how to find them again.

It's all quite an adventure.

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84 300SD
85 380SE
83 528e
95 318ic

well i finally got the new thermostat in and my heat is still wonkie, i tested the connector at the monovalve(which is new) and it would get between 0-14 volts, so i know power is going to it,when i unplug the monovalve i get heat until i hit about 1200 rpm,(on the road or in the driveway)then it blows cold air, if i dont run the fan i can get warm air to seep out of the vents, but when i turn on the fan it starts to cool down real quick.
would vacuum increase with rpm, making a flap open/close when its not supposed to? when i connect the monovalve i will get heat untill i start to drive, then it will blow cold,i am pretty sure my ccu is working because with te monovalve pluged in i could control the heat with the temp wheel, but when i went to the colder end it would then not warm back up

I sold my 380sel, so I'm just lookng at my repair manual. It seems like a posible cause maybe no coolant flow through the heat exchanger.

The repair manual says that the monovalve shoulld have > 11 volts with the ACC set to off.
It also says that the auxiliary coolant pump should have > 11 volts when the ACC is set to defrost and if it does, touch aux coolant pump to verify operation.

I believe that no (or limited) coolant flow through the heat exchanger would give the problems you describe.

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07 E350 4Matic wagon, 06 S430 4Matic, 99 SLK 230
retired W210 (x3), W124, W126

Earl,
This is a cut/copy of a post by cbrown888 that deals with the same problem you have.


"I have an 85 300Sd that I have been going over a year with no heat. Finally cut the bottom rubber seal off just to get through this tough winter.
I have replaced virtually every component in the system including w/pump. aux pump, temp control unit, pushbutton set, in car temp sensor with aspirator pump, water pump, t/stat, cap. Had tried several used mono valve magnets, replaced valve with MTC unit. Still no heat at highway speed only at idle.
With everything leading to mono valve I bit the bullet and bought a new mono valve assy from the dealer and used only the magnet and plunger and guess what the heat works like a charm now.
I am suspecting that the combo of the MTC plunger and the magnet coil loosing effectiveness because of exposure to heat, moisture and age they are going bad. I tried 3 different used coils with the same effect.
I also compared the MTC plunger to the one in the new mono valve assy and talk about a difference in construction. The Bosch new has a stronger spring and thicker rubber.
Now I have heat at the temperature I want not either on or off. There are alot of good aftermarket parts out there but these MTC plungers are junk "

There are some bad parts out there and we need to be careful what we buy and especially where it was made.

The only test you need to do at this point is warm the car up, press the defrost button and see if you have heat at the windshield. In defrost, the system needs NO vacuum, the fan go to high speed, and the mono valve is turned off (Open) and the aux pump is turned on. The aux pump is not really needed. It is unhooked on both of my cars. If the engine temp is above 40c (104f) the air should be warm. If not, the problem is most likely the mono valve.

Paul

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84 500 SEL (307,xxx miles)

I can't remember exactly, but I did have a problem with my heater on an 83 380sel and it was the monovalve. As I recall, my symptoms were excessive heat (my blower just worked hard to try and cool, but it just blew really hot air). I removed, inspected, and reinstalled the valve and the problem went away for awhile. When the problem returned sometime later I disassembled the valve and found that it did not move freely when power was applied. I cleaned it to ensure that it moved freely, reassembled and never had another problem.

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07 E350 4Matic wagon, 06 S430 4Matic, 99 SLK 230
retired W210 (x3), W124, W126

thanks for the reply's i was wondering if the magnet in my monovalve was bad, i tried to contact someone on here about a monovalve magnet but have not heard back , i will do the defrost test today, anyone know a good source for this magnet ?
kenny

so..driving home last night with the mono valve unplugged i got hot heat from the defrosters until i got the above 1200 rpm, this morning drove to work with the mono valve plugged in and i would only get hot heat out of the defrosters if i were stopped when i got to work i would have heat when stoped in my parking spot but as soon as i brought the rpm above 1200-1500 i would lose heat .all this while sitting still

update, i bought a used mono valve (the whole thing ) and swapped out the magnet along with the insert from the used one i got in the mail, and now my heat is back to working as it should, the mono valve that was in there(which was a week old) looked ok, no rips in the rubber, but it did not work it turns out, so i guess the magnet was what was bad?

The magnet or a sticking magnet could have been the problem. You might be able to test it outside of the car to see if you can replicate. It may be worth keeping the old unit for pieces / parts if you can troubleshoot and repair it. Glad you got your heat back!

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07 E350 4Matic wagon, 06 S430 4Matic, 99 SLK 230
retired W210 (x3), W124, W126