Automatic Climate Control
 

I feel embarrassed to ask, but don't have my manual with me and on a trip. I tied finding a manual without success.

Is there only one setting for defrost? It was blowing high and hot which makes my eyes uncomfortable so turn it off, then wait until it fogged to turn back on. Even tried turning the floor vents on to keep the cabin warm, but...

How does one get the automatic mode to work? There is no light that comes on/goes off, and even with the temperature turned down, the heater doesn't go off.

Thanks in advance! :D

On my 126 the defrost is always on max blower and heat when selected. When set for economy heat the leg room vents are open and there is a small flow of air to the defrost, at the selected heat temperature.
If you do not have any warm air flow to the defrost area when in the heat mode there may be a problem with the vacuum pods in the heater.

Thank you for the help! :D

So with economy, the automatic climate does not work? So then set it to normal then?

Next time I use her, I will see if I feel warm out the defrost. The pods were replaced, so should be fine.

I'm not certain I am following this exchange, so here is another $0.02....

When defrost is selected, the system should operate at full heat and highest fan setting out the defrost vents only. There is no auto temp control and no way to reduce the heat output. That is how the system is designed.

In all other modes apart from defrost, you should be able to choose between manual control of fan speed or the auto setting, which operates the fan in concert with the auto temp control. You should also have auto temperature control, based on the setting of the adjustment wheel. Economy mode only differs in that the AC compressor engage on that setting.

In every other mode other than defrost, if you are selecting a temp and the system isn't shutting off when that temp is reached, there is an issue with one or more components.

Zacharias, thank you so much for your help! :D

So I am doing something wrong. How does one know when they are on the automatic setting? What does it control, fan speed AND temperature?

Sorry, when I read the thread the first time I thought it was you who mentioned a w126. I now see it was the other respondent.

You always need to specify the model and year of car you are asking about.

I doubt you are doing something wrong. Assuming for now this is a w123 or a w126....

When you
1. push any button except defrost or 0 (off) and
2. set a temperature setting on the wheel, and
3. push the middle button on the fan speed controls

The system should maintain the selected temperature (fan speed will increase while the interior warms up, then automatically slows when the selected temp is achieved).

If this is not happening, there is a fault somewhere in the system.

In fact, the air conditioning compressor engages in all operating modes except Economy.


The ACC does not "shut off" unless the OFF mode is selected.

1. I meant to say "does not engage"

2. I think my post #6 clarified what I meant when I said "shut off".

For some reason missed the reply... Thank you all for the help! :D

Zacharias, sorry I forgot the information was not available. I am used to it being in the signature, which I apparently forgot to put. F.Y.I., this is in regards to a W123, specifically a 1985 300TDT.

What I am doing wrong is assuming once the desired temperature is reached, the system shuts off. Instead, it only slows down the fan speed. So, automatic only means automatic fan control, rather than full temperature control?

Again, how does one know they are in the automatic mode? There is no light like the other buttons that I can tell...

So why would the compressor turn on when heat is selected?

As far as I know, there's two reasons why the AC compressor would run even during heat output --- one, the air is probably still pretty moist (even if its cool out) and you dont want to put hot moist air on a cold windshield, and two it keeps the compressor lubricated so the seals dont dry out, leak freon and become a engine christmas ornament like mine is right now.

I would not expect the compressor to act as a dryer, but if so, that is quite fancy! Good to keep in mind if one is trying to make it to the next station! ;) :P

Too bad about yours, but good to know they can dry out. Mine is brand new, so hate to shorten its life. ;)

That's the way the system was designed. If you don't want the a/c on, push the EC button.

That is precisely why the a/c runs in the defrost mode. More precisely, the drying occurs at the evaporator, not the compressor.

I don't mind, just want to understand. ;) This system is quite fancy compared to even modern systems like my Grandmother's 1980 Buick. All it has is automatic temperature.

What I still don't understand is how does one know they are in the automatic mode?

If the system is working properly, the fan will stay on all the time, as you mention.

The push button you select will be brighter than the other buttons.

These units fail, so if you make a selection and nothing happens, after a delay, then it isn't working.

Thank you! So then, maybe the light is out? The system has been gone though, so thinking I must be doing something wrong...

You're welcome.

It has a few light bulbs, see sockets in pic.

How does one remove the switch? Is it still available?

watch this video. relevant section starts at about 2:50
Mercedes Benz 123 Chassis Center Console Wood and Switch Removal by Kent Bergsma - YouTube

you'll know if the automatic control is working by pressing the small button so that the high and low fan selection are both popped out. the automatic control should vary the fan speed. it will never shut off. it will also vary how much heat comes out of the vent. in using mine, it feels like the farther away the target temperature the hotter the air coming out of the vent. the system is very slow to react, by the way. i dont know if thats how its designed or because its 30 years old.

Thank you so much! :D

I will watch it, but interesting you say the automatic pops, as mine doesn't, thus why I was wondering how one knew what mode they are in. Now what?

I found it interesting how far the automatic button sticks out in the video. Mine is missing most of the lettering. What is the unit called? I am thinking of finding a different unit...

It's an Automatic Climate Control unit.

Yep, thank you, I realized that late last night doing research. I thought the switch was separate but in fact part of the whole unit. So that ends getting new and maybe used. In the end, it does work better than nothing! ;) :D

The way you phrased that, I'm not sure if you understood what the other respondent meant by "pops". When you press the automatic button, if either of the manual fan control buttons (above and below it) is pushed in, the manual button should pop out when the auto button is pushed. The auto button doesn't stay pushed in like the others when it has been pushed, it's a momentary switch. Neither does it pop out when one of the manual buttons is pressed to take the system out of auto mode for fan control.

If you do need to replace the unit, auto climate control units new were nearly $400 last time I checked. I would suggest you put a 'WTB' (want to buy) posting on the Mercedes Used Parts for Sale subforum (accessible off the main forums page). Lots of folks have parted out w123s over the last few months so someone probably has one lying around for a more reasonable price. I would recommend that you get a unit out of a w123 -- the early w126 series unit looks identical, and some people say they have interchanged them, but technically it isn't the same. (The w123 part has 123 in the part number.)

BTW, sorry if I came across like a hard*ss in my reply yesterday to you about including model info in posts... likewise apologies to querty for snapping at him. Three days of meds for lower back immobility tends to make me snappy (and causes me to make typos, as querty was pointing out).

Zacharias, thank you so much! :D

I got it now. I thought it was a momentary, but others said it "popped" like the others.

In my research, I found new units are no longer available, only rebuilt. Price range from about $700 for a Mercedes rebuilt unit to about $165 for ProgRama unit (which appears to have the longest warrenty at three years and unlimited miles). Core is around $25 so shouldn't be hard to get a used unit for about that (I wouldn't pay more than $50). For now the plan is understanding, which has been accomplished, then applying Bounty sheet to the inside of the glass to keep down the fog eliminating the need for high heat. ;)

Some folks have success in reflowing any failed solder leads, referred to as a cold solder.

Adriel, you should have either brought your owner's manual with you or Emailed me about this.

The way we always did it was "defrost" until the windows were clear and we were roasting, then adjust the temp wheel to a comfortable setting and press the button with the solid white up and down arrows. This allows the air to come out and windshield and feet, and will keep the W/S clear without roasting you out of the car. If you're running in high moisture, rain, snow, etc. use the high fan setting, otherwise use Automatic.

And yes, the A/C system is activated in all except the "EC" (Economy) mode since the A/C system is also a dehumidifier.

X2

Tram, danke for the help! :D

For the record, I didn't do it your way, but think it would work better: high fan for moist weather. What I do was turn the defrost on until clear, then turn the floor vents on until reduced speed and needed to turn the defrost on. I don't like warm air in my face but love hot feet/legs. If the defrost is bothering me, I open the sunroof and not only cools my face but actually helps clear the windshield especially if only cracked open. I find with just the floor heat still comes out the outermost vents. I discovered these are for clearing the side windows which is even more critical than the windshield as Ember likes to rest her head on my shoulder and fog the window! :rolleyes: l.o.l.

It seems if you have it in automatic, it stays in automatic despite taking the key out. Is this the case? How does one tell it is in automatic?

The system did have a hiccup shifting from 26*C to 22*C, so turned it to max cold which reduced it from hot air to warm, and cleared in a few minutes. Think part of the issue was the passenger floor vent was blocked with all the stuff in the wagen and had to clear the hot air.

Over all, I am trilled with the system! :D It is harder to fall asleep or get too cold, as on 22*C it is a nice soft cool air not some gale force that dries ones eyes out and causes icicles to form. The system is nice and logical, it doesn't have some abstract diagram showing warm to cold, it actually tells you what the temperature is! :D If you do get a tad sleepy, just move the wheel ever so slightly cooler and the fan will speed up and cabin will get colder. Grab something to crunch, and even more set. ;) A very fine highway auto.

Running the compressor for defrost is the standard method on all cars of any brand with ACC and even some with manual climate control. The evaporator removes moisture from the air. Very useful for defrosting a windshield.

In the Southeast, i consider working a/c a safety feature especially in the fall and winter. We get chilly rain and if you cannot dehumidify you will completely fog up on the inside in short order.

Operating the compressor frequently is beneficial to its longevity. If it sits idle the seals dry out and it will start to fail.

Side story: I have a 2004 Honda CR-V that has a manual climate control. There is electronics involved but you still have to choose the modes and temperature yourself. I found on a Honda forum an Easter Egg that lets you choose whether it automatically engages the compressor with defrost or not. For some reason the default setting is "disabled".::confused:

Larry, thank you for the information! :D

So then why do some folks with the other cars get better mileage in the winter? They claim it is because of not running the A/C. In the other car I had, it did get a tad better. Maybe the cold air?

Guess we are fortunate that we can turn off the compressor, however...

Operation in the winter prologs its life, interesting! :thinking:

So the South has humidity all the time?! I was there in about the hottest part of the Summer and couldn't stand the humidity! Like existing in butter and feeling like it rained as your cloths are all wet. But then I was child then, and might be more tolerant... Probably the Honda has it set that way because Japan doesn't have humidity. ;) :rolleyes:

Adriel: Jay Bob is correct about running the A/C being good for it. Even back in the ACVW days, when you could buy dealer add- on A/C, the A/C manual told you to run it for five minutes at least every week during the winter to keep the seals lubricated and supple. Same with the old Frigiking and Kuhlmeister add- on A/C for Mercedes from the '60s.

Without that periodic lubrication, the seals can shrink and fail.

Really? Guess the A/C compressor from a type 3 was junk then. Good to keep in mind when getting used parts. Guess one could get anal and panic when they have to leave the auto behind for more than a week! ;) l.o.l.

If the seals go, any way yo hydrate them?

How does one add just oil?

The seal in the old York compressor and the GM A6 is made of carbon with a spring loaded pressure plate. The R-4 can have either a carbon seal or a lip seal, depending on vintage and application. I haven't seen the 'O' rings deteriorate until recently, when lots of shops started using the cheap 'O' ring sets from Harbor Freight.

Use the green 'O' rings from a reputable source...FWIW