Heater working on/off in '87 560SL - Page 2 - PeachParts Mercedes-Benz Forum

2quik6 · #16 12-22-2007, 04:57 PM

hmm, I took it apart and the valve and the rubber seals all look to be in fine shape....if they were damaged, that would cause it to not seal off the passage and cause heat when you didn't want it.
The original problem was that it was not heating.
I also see that the valve when at "rest" makes the coolant passage open so that water flows to the heater core...so why it continues to heat when it has 12v and ground when the wheel is at "max" makes absolutely no sense to me...not to mention that its getting ground when on "max".

So I'm assuming now its not the valve at all but something else, either the temp control unit or the temp sensor. If it were the valve I'd be getting heat when I didn't want it, it would appear as the valve could not seal off the passage of the coolant to the heater core if it were bad.

BTW, if it matters, the heat is coming out of the center vents only. The sides and floor are not blowing anything.

Thanks for all of your help thus far.

ctaylor738 · #17 12-22-2007, 04:59 PM

Sorry, I mis-read your post.

So if you are getting ground at max heat, then I would say that the heat control has gone TU as well.

But still, if you are getting hot water to the heater, you would get heat in the cabin if the flaps are in the correct position.

If you end up needing a new control unit, Programa sells rebuilts for less than $200 through several online vendors, and it's an easy DIY replacement. If your mechanic goes with Mercedes parts, you are looking at over $750 for a new one.

Chadahar · #18 12-22-2007, 05:02 PM

With the Mono valve unplugged it is in fail mode and fail mode is open to provide heat all the time for defrost purposes. Sounds like your mono valve IS working as designed. Though it may be sluggish from not being used in warmer times. Remember +12 = closed valve and is closed when heat is NOT on, +0 = open (or fail mode), when heat is ON. It works off the Ground instead of +12V....backwards from about anything else electrical.

CONRAD · #19 12-22-2007, 10:48 PM

I read this thread with intense interest?
I have a 1985 380 SE.
My heater simply stopped blowing/providing heat.
I bought a heater control unit ( includes the climate control wheel
and the 5 push horizontal buttons and the 3 vertical fan buttons).

Now.....

How to remove the unit from the dash ?
What's the technique ?
I need to know exactly how to remove the unit.
There are no paper service manuals available.

Somebody knows how to do this.

I need to know. It freezing here in Northern Calif-95245.

Many, Many tks.

Chadahar · #20 12-23-2007, 12:08 AM

Whoa up a bit. Heater quit or blower Quit? You need to know which. if you put in a new CCU and the blower motor is dead it'll also fry your CCU.
To find the heater plug you have to remove the passenger side bolster, kick board(right(covers the Computer brain). then the plastic foot well cover. then remove the glove box. In front low to the left is a vertical plug. This is the fan plug. unplug the fan and check the terminal pins one is hot and one ground and the ground wire will have brown in it color combo. Ground the ground pin and put +12V to the hot side to check the fan. It'll blow at highest speed. If it works well and not noisy or slow, then it's OK. If not replace it. Reassemble the bolster, foot well cover and the left kick board.

Next. Unplug your Aux water pump as it probably failed and fried your CCU(the one you are replacing). AWp plug is next to the battery towards the driver side in a clip un clip the plug and disconnect. Then check the mono valve to see if it is ruptured, that could be you no heat problem(do you have heat all the time through the defrost and bottom dash vents(when moving), if so your mono valve is probably ok but check it anyway.

CCU removal and replacement
Now to remove the CCu unit from the dash.
1.remove the ashtray from the holder.
2. then take out the two phillips head screws that hold the ashtray assy in place. (bottom left and right of frame.
3. reach in under the radio and pull forward until the locks in the forward edge of the housing release. Pull radio out.
4. unplug everything from the radio and unbolt(10 MM I think)) ground wire. (take out the long black plug on top first then the rest.
5. There are 2 phillips head screws above the radio slot. Take them out and gently pull on the dash, slightly up and out to release the two prongs that hook into the CCU above the buttons.
6. pop the top switches out of the dash. unplug them and keep in a safe place. remember which has two lights in it(brass plugs separate from the plugs). now you dash is free.
7. unbolt the two bolts above the CCU (8MM) a flat 8mm box end works better than anything else). Loosen these bolts. Slide the CCu out.
8. unplug the right and left plugs from the side of the CCU
9. go to ProgRama website (http://www.programainc.com/?go=technical_support&v=3)nd look for your number of the CCu(on bottom door )(1985 will be the same as my 1984)
Look for this number in the downloads (126 830 0285 (60285) ) This will tell you how to perform the test BEFORE you install your new CCU. Do it just like they say.
10. install new CCU in reverse order of removal.

I've done this job 3 times in the last month on my car as i couldn't find the AWP plug and unplugged the mono valve instead. Smoked two CCU's. By golly I know where they are now!!!

2quik6 · #21 02-22-2008, 12:30 PM

FYI, I meant to post this up a couple weeks ago, the shop I took this car to when I first got it to have other things repaired, also repairs some other car s I have, my LT1 Trans Am...anyway when I went to pick up the TA from having the transmission rebuilt I told Jack, the owner about the heater issues with the 560SL. He said it sounded like the control unit, and gave me 3 different control units he had to take home and try. Said they should all be good, but were laying on his shelf and he didn't need them at the moment.

Took them home and the first one I swapped in worked like a champ!
Been working great ever since and didn't cost me a dime, now that's Customer Service!! He also explained how to take the control units apart and look for broken solder connections at certain places that are common if I wanted to repair the one I had. I got the back off the bad one but still didn't find anything broke in there, but would have been an easy solder fix it there was at appeared.

Been working great for several weeks now!