88' 560SEL - Today, suddenly no Heat?

[Aaren]

Ok, so this weekend i was swapping in a new stereo, plus dash and door speakers. In the process I pulled apart some of the under dash on the passenger side, plus enough of the dash to work on the new stereo.

Afterwards everything worked and the defrost had good heat coming out of the dash.

This morning driving to work I had heat from the defrost and after 10-15 minutes of driving switched the heating from defrost to straight heat. At this point cold air started to come out and I switched back to defrost, that was now cold air as well?

Is there a chance something I did, or some wire I ran snagged somewhere under the dash on something and cuased this?

I assume with eletronic dash switchs for the heat, they must trigger an electric valve somewhere else that mixs the hot and cold air etc.

Anyone got any ideas or a good game plan on where to check. Still to early in the year to not have heat in the monrings!

Thanks all, your previous answers have been incredible.

[MBL87560SEC]

Hello Aaren,

I think you'll discover that there are several vacuum actuators that govern airflow & temp blend on the heater unit. There is a control unit who's solder joints somtimes fail....

There are many ACC threads in the archives that will be of benefit to you.

From the Search Tool: http://www.mbnz.org/forums/search/query.asp?keywords=acc&searchforumid=12&author=&da ys=&action=search should get you started..

Cheers, MBL

[Aaren]

Following that link you suggested and doing some other searchs of my own I noticed lots of discussions about the monoblock valve and it's eventual failure. I ran out last night and identified that unit.

This morning was identical to yesterday. Surprisingly the defrost came on hot and fast. After 10-15 minutes of driving I turned it off. After 5 more minutes or so I tried to turn on heat and got nothing but cold air again. Cold air was coming from heat and defrost settings both? But, after I stopped at my usual coffee shop and turned off the car. I noticed that once I was on the road again defrost was working again with heat? So maybe it has something to do with turning the vehicle off? The vaccum resets or maybe this monoblock valve?

Does that help? I know forums and I'm familiar with the preference to search forums before asking questions that may have already been answered, however this site the search often times out and results in nothing so after a few tries, I just post the question as new.

[Aaren]

So doing some more research I see the Climate Control Unit is built into the dash with the heating / cooling buttons integrated into it. Is this an item easily opened and serviced for these solder problems mentioned? I rebuilt my drive seat control unit the other day and was shocked when I opended it and tiny pieces and bearings fell all over the place. But, I put it all back together and now it works properly.

The monovalve seems a much easier fix and the repair kit mentioned in the forums is much much cheaper to install rather than replacing the unit which seems overkill.

Does all this make sense to those "in the know"?

[Ears]

Aaren - 3/7/2006 10:41 AM

So doing some more research I see the Climate Control Unit is built into the dash with the heating / cooling buttons integrated into it. Is this an item easily opened and serviced for these solder problems mentioned? I rebuilt my drive seat control unit the other day and was shocked when I opended it and tiny pieces and bearings fell all over the place. But, I put it all back together and now it works properly.

The monovalve seems a much easier fix and the repair kit mentioned in the forums is much much cheaper to install rather than replacing the unit which seems overkill.

Does all this make sense to those "in the know"?

I think your unit is close enough in appearance and function to mine that I can comment. Yes, the unit is relatively easy to get at and open up, but I don't recommend it, unless you KNOW it is bad. Then you have nothing to loose. Replacements (rebuilt) are available for about 250US bucks plus core/exchange (read Germanstar), complete with new fan switch and temp thumbwheel, I believe. Since you are testing with the defrost, I believe your problem lies in the heater valve (monovalve). I'd start there. When you dissamble, you'll probably find the diaphram ruptured, or the screen mesh filter crushed/blocked or both (as was my case). Using defrost to test should allow you to bypass the temp control; however in case I'm wrong, perform your tests with the thumbwheel on MAX heat, econ mode. I think what was happening to mine (and it was doing just as you have reported here) was the plunger was becoming water/hydraulic locked, and not able to re-open until the flow of water was shut off and the pressure relieved.

Let us know how it goes...

[Aaren]

So, final verdict was the Monovalve.

I put in the repair kit in about 15 minutes and now the climate control is just purring along perfectly.

Great fix for under $70 CDN. I know they are about $35 US, but with shipping and duty fees at the border I opted for a local part in stock and a few bucks more. I'm going on a trip this weekend and it's well worth the effort.

Thanks to everyone who contributed!