The fan (easy to test with jumpers, at least at full, 12v setting) or the resistor, located on the firewall, usually pass side in engine compartment.

My wife can fix the CC unit easily! Why?
 

OK, I've been reading and posting on the forum for a couple of months and I've got a good understanding of the dozen or so problems and how to fix them including resoldering the CCU. Just need more wrench time.

For years, our 83 300D has had a tempermental CCU that works sometimes. Today it was the defog windshield that would not come on (no fan at all). For years now, my wife fixes these problems by shutting the car off and restarting - problem goes away about 75% of the time. It makes no sense to me why that would work.

After about 10 minutes of her nagging today, I pulled over turned off the engine, waited her prescribed 10 seconds and restarted. Defog can on immediately and worked the rest of the way home. She even cycled it to regular vent and back based on fog and temperature needs.

The only way I can contend with her smug "I told you so look" is to come up with an explanation as to why her method works.

Please help - the masculine dominance in car repair needs redeeming!

Charles

This sounds more like a blower motor problem, rather than a CCU problem. If the blower motor brushes are extremely worn, you will get just the problem you are describing. Replacement brushes are available at www.**************.com but if the commutator is worn, you will need to change the blower motor.

Already changed the blower assembly.
 

That was my thought a month ago. I found a good assembly at the bone yard, replaced the brushes, commutator looked fine. No change in random behavior.

But why would turning it off and back on change anything?

The CCU pushbutton unit mainly controls the mode of operation and temp. selection.
The Blower Speed Controller and of course, the blower itself, for airflow.
Then there is the Temp. Controller for using inputs from the CCU and Temp. Sensor to control the blower speed, monovalve and a/c compressor via the pushbutton control.

Is only the blower cutting off? or is it not changing modes? or do you lose control of temp.?
Turning it off to reset could be a heat factor with an electronics assembly.

Not sure of mode
 

With the blower not running, it's hard to tell about mode but I don't think it is switching. The pushbuttons seem to do nothing. There seems to be no control of temperature. There is a little warm air coming out the vents but not with fan assistance. I think it is bringing in outside air over the heater core.

Have you checked fuses?

Have you opened and resoldered the CCU Controller?

I guess I don't understand what you have done so far to resolve the problem other than change out the blower motor with another used one. BTW, I went through two used blower motors in short order (less than 6 mo.) and decided to put in a new motor and be done with it.

Sam,
Most of the fuses are the originals (25 year old and aluminum). I've ordered the new style brass ones and will replace all as I clean terminals.
The CCU was resoldered about 3 years ago.
I've got low vacuum and a noisy pump - replacing it this weekend and then checking for vacuum leaks.

I've got a plan and I'm sure I'll get it fixed.
Question is:
"Why does killing and restarting the engine make it work"?
Often if the system is working and you stop and restart soon, it will quit working. This is the baffling part that my wife is so smug about because her method works and I can't explain why.

Charles

PS: What's the trick for removing the plastic fan without breaking to replace the motor? The entire assembly new is too expensive. The motor is reasonable but it looked like I would probably break the fan trying to remove it.

Well, I don't know if I can completely explain why shutting it off and restarting causes it to work. (And having been married before, I know that you will probably never prove your wife wrong as long as she thinks she's right, in her own mind.)

With the vacuum pump marginal and fuses on the edge, resolving both of those issues may do the trick to cure the intermittent problem. Check those fuses closely as I had one that gave me fits because of a hairline crack where the end cap met the fusible strip.

To remove the fan cage, support the cage really well on two sides and a good whack with a drift punch causes it to drop right out. Be sure to have something to cushion the motor when it drops as it usually comes out with one blow. (They must build both of those parts with very exact tolerences to cause a "press fit" to be so snug.)

Ignition switch was the problem
 

Now that I've found the problem, it all makes sense. I was not always getting current through the ignition switch to various switch on features including the CC system. Problem seems to be solved with new ignition switch.

I don't thing I've seen that listed in CC issues.

Charles

time to get the soldering iron out....my AC weirds out on me and switches to the DEFROST vents; turn off ACC for 5 seconds; turn back on....and vents switch from DEFROST to DASH. Weird. Glad you guys have already gone thru this ahead of me....would drive me crazy.

I posted in the parts section two used ones that I was trying to solder if anyone wants to buy them to play with or for cores.

Mine was the ignition switch
 

Mine was doing this and I replaced the ignition switch to clear up strange problems like dash inicators coming on at odd times. Looks like it cleared up my weird acting CCU also.

My theory (open to comment and revision) is the ignition on position supplies current to the CCU. If this was interupted by sporadic shorts in the ignition switch, the CCU would be getting current on and current off signals causing it to be confused.

Plausible?
Charles

I have a few extras that I was going to resolder, but I bought a rebuild programma one. I have the extras on ebay, item # 220235685135

So you guys can play with them. $0.99 start bid, ends this weekend to be fair to everyone that cant log on during the business day.

I drive a 1989 300sel (126? )

OK i need some help this is driving me crazy, the climate control seems to have a mind of its own, it seems unwilling to change what its doing. IE Ive had air conditioning running now for 5 weeks, before that i could only get the heater running.

so far i have not tried that much all i have done its pulled the climate control module out and done a blanket resoilder of the hole board (part number 1268300885)

It used to be that you could get the climate control to change by switching the climate control off when the motor was running. then turning off the motor, changing all the setting then starting the motor again but that no longer seems to help

sometimes when i start the car it seems to think about putting the heater on (you know how it seems to like blowing air at your feet when its heating and blowing air at your face when its cooling.....) but then it stops for a second and then i think it starts the compressor, i can hear the load on the motor

as a test i disconnected the mono valve and now i think i have the air con running and the heater at the same time (the temp wheel is set to max heat)

oh most of the system is working i can adjust the fans and i can put demisters on and i can turn it off the only thing I'm having problems with is temperature. the temp wheel seems to do nothing




now the things i think it could be after reading all of your posts

1/ ignition switch -seems very odd and i think mine has been replaced all ready but did they stuff it up some how?

2/ The push button climate control module its self - even though i have resoldered all the joints i still wonder about that Potentiometer (the temperature wheel) maybe its intermittent ?

3/ the device that senses the temperature in the car - think this is the most likely culprit but don't know were its located any one know ?


is there anything i could have missed ? thanks for any help

I believe your car has several differences from the original W126's so you will need a little different information and schematic. I believe this may be a procedure to help you diagnose your particular vintage: http://www.peachparts.com/shopforum/1546012-post70.html

thanks for your quick reply. I think that link is mostly to do with problems with the air conditioning not working at all and I don't know if it will help work out what system my car has. but I can all ways check every thing on that list

this is a picture of my push-button control unit

I believe the temperature controller is located above the passenger footwell. Do you have a copy of the factory service manual or more specifically, the schematic for your car? IIRC, yours has a small sampling fan that draws air across the sensor for better response to temp. changes. Also, the pushbutton controller was changed in 85 or 86 to a new version.

Another note, have you checked the fuses? The aluminum ones are notorious for causing intermittent problems. Use the copper ones if you can find them.

You might find someone in the Tech Help section of the forum that is more familiar with the nuances of the later 126 series climate controllers.

Problem loading page showing DIY for solder fix
 

My '81 300SD climate control isn't working and I've checked the fuse and blower motor and replaced the control unit with a questionable one. It worked for a short period then stopped. Winter is coming to Iowa so I thought I'd try resoldering the board but couldn't load the DIY page. Could someone send it to me? Thanks a lot.

Describe "isn't working". Typically, resoldering is for symptoms of no mode change, ie. defrost only. If you just aren't getting heat then the usual culprit is the monovalve.

Hi
could this also apply for the cliamte control panel of W116 , 300SD ? I also only have warm defrost and no other knobs are working. Can not regulate heat either.

I believe the W116 is different, and I'm not sure about the Euro model, as they have the servo. If you do an advanced search for "servo" here on the forum, you should be able to find more information. Especially check the DIY section articles that come up in your search results.

(Advanced search is found under search on the header bar at the top.)

Thanks, I´ll search. It´s a US model returned to Europe.

Ok I have run into one of the problems you describe in here.

Does anyone have some pictures or something that can guide me on my way, to find this foam hose, so I can figure out if it has been crushed?

It should be said, that my car is a 1987 300 E Euro model, with a manual dual zone system. One for the drivers side, and one for the passengers side.

Thx.

Never mind, found it and it seems to work fine.

There is suction, it is not a whole lot, but it is there.

But that just leaves me even more baffled, but now it is time to do some measurements on it, to see if actually works.

I have the blower on and nothing comming out thing will sodering help this problem

Maybe, have you eliminated other possible issues such as bad fuse, bad blower motor, bad resistor, etc?

You can here the blower going but nothing comes out! Fuse is good!

If the blower is going, air should be coming out somewhere. Determine where: defroster, foot vents, dash vents, etc. What model car?

Yup I checked everywhere no air comming from any where. Its a 1988 W124 260E

I don't know your model. If it were mine, I'd start by opening the blower assembly to 1. Be certain the fan cage is turning, and 2. Begin looking for blockage. Seems to me if the cage is turning, it should be moving air, and it should be coming out somewhere inside the car.

Anyone else that knows this model have an idea?

Maybe you'd get more response it you started a new thread with the model in the title.

I have the same problems on my 84 300SD Turbo. It has 2 push buttons and it looks like the lack of spring pressure is not allowing the switch to come out all the way.

I have the problem of an intermittent fan which has a mind of its own. It likes to go on and off whenever it wants. One of the bad push buttons is for the "Fan High" and the other is the center button on the ccu for "Bottom airflow".

I am in the process of re soldering the boards but I would love to be able to FIX the buttons without purchasing a complete ccu. Any help would be appreciated.

One thing I thought of doing was to epoxy a small ring or to drill a hole in the shaft to stick the end of the spring in, but I thought I'd ask before I make matters worse. :confused:

W123 Blower Resistor (83 300D)
 

Could anyone tell me how to test the resistor? Apparently, it's the weird looking metal cage thingie with coils in it on the passenger fenderwell....

Pretty simple, just unscrew it so you can see inside and test the terminals with an ohm meter to make sure there's continuity between the coils that connect to terminals. In other words, trace out a coil from where it starts at a connection terminal to where it goes to another terminal and measure the resistance. There shouldn't be any noticeable. It's pretty obvious when they go bad. You'll have infinite resistance and usually see it broken.

I have some of these (used/good) if you need one.

I took apart a spare climate control p/n 123 830 12 85 down to the PC boards to see what's inside. There's 4 relays, a few resistors and diodes that's it! There are no IC's or transistors. I wouldn't call this thing a computer. Will post a pic later. What I plan to do is run this thing naked and see which relay clicks when the switches and temp dial is operated. The pdf I have of FSM 83-601 Manual and optical function test of automatic climate control has a wiring diagram that is illegible. Does anyone have a legible copy they can send me?

This page may help for info on what to look for/some troubleshooting steps:

http://userweb.windwireless.net/~jimc/mamerepairs.html#acctest

No pdf's there, just electrical troubleshooting info.

I'm not sure about the part #, but I believe the W126 and the W123 are the same for several years. Here are some for the W126:


Hmmm. The main electrical pdf is too large for an attachment by about 500 bytes. If these are what you are looking for, I will try it as a zipped file or some other method. Let me know.

Thank you BoostnBenz for a DIY that will stand the test of time. I attempted this last night. Fail. Now my vents shoot 120-140 degree heat with the AC on and temp selector set to "MIN". I was careful not to join two solders, so I think. Where do I start troubleshooting this? I can be emailed at zn24(at)aol.com

Thank you for any help.

Bump for help. I'll be redo feeing my ccboard this afternoon, checking the resistor, and hopefully testing the blower motor. Where is the electric connection on the motor for me to hook up directly (to ensure it works). 1982 300tdt, 160k miles.

I've also not found a good DIY of the blower replacement, anybody found anything with sharing?

Blower motor is cake, remove the kick panel (us a thin, small screwdriver to "pop" out the screw covers to avoid breaking them, they can be pretty brittle), remember the grey 1/4-turn plastic panel screws, then pull in on the black plastic that protrudes into the vent to pull the whole panel out. The motor is on the right, three 8-mm headed screws and usually one phil head lets it drop down. D/C the wiring. That's it.

Sometimes blowing the junk out of it "fixes" it.

Today I started with small and easy to fix. The resistor pack checked out well. I checked the fuze, and found a mess of corrosion on all the fuzes and accompanying connectors.

A wire wheel and dremel later, and my tach is working again, and so is the blower. Well, it mostly works. Only when the cc is on automatic, and the top and bottom vent button pushed does the blower work. If either of the other fan buttons are pushed, then the blower stops. If I press the defrost button the blower stops as well. Moving the temperature controller away from max tetmp sometimes makes the center console behind the controls hiss a bit, and the fan to slow or stop.

I'm going to do the work on the cc unit, and then see. I mighty be lucky and this might fix my problem with heat.

Now all that's left is the proble of all the small holes nibbling at my car.

Patbob
Thanks for the detailed pics. I also visted your blog site great information a great help for 10 thump newby! I have '82 300SD. :):):):):)