ACC Question 1983 300SD

[tr1cky]

The fan switch as we know has three buttons, high, low and auto.

When I press the Auto button it does not hold, as in it doesn't click in like the high and low fan buttons will. It will cancel either low or high, whichever function was being used, but not click in.

Questions:

What is the proper effect of the auto button?
Is it supposed to click into place?

[rrgrassi]

The proper effect is to control the fan speed based on air temp at the sensor and temp selected at the wheel.

The Auto button on my car does not "click" either.

[leathermang]

My 1981 wagon only considered those buttons as ' Mild Suggestions from the driver' and felt free to ignore or wait 20 minutes to respond....
I suspect the canceling of the low and high is proper...
what it relies on to act I am not sure off hand.
Try turning the temperature regulator farther one direction or the other and give it some time to see if it does in fact come on in response to that nudging...

[Graplr]

This is normal operation for this button. AUTO means exactly that. The ACC will automatically control the car's temperature based upon the wheel setting and ambient air temperature. It takes awhile for the AUTO setting to kick in (meaning NO button is depressed on the PBU) and the fan to start but it does. The heating and cooling are iffy at best in my car so I almost always have FULL heat, FULL air, or OFF depending upon the season.

[tr1cky]

Originally Posted by Graplr

This is normal operation for this button. AUTO means exactly that. The ACC will automatically control the car's temperature based upon the wheel setting and ambient air temperature. It takes awhile for the AUTO setting to kick in (meaning NO button is depressed on the PBU) and the fan to start but it does. The heating and cooling are iffy at best in my car so I almost always have FULL heat, FULL air, or OFF depending upon the season.

I shouldn't be too greedy here as I have great heat and ac and proper vent functionality.

I haven't used the auto feature, mainly because I assumed the auto button was supposed to remain depressed and assumed because it was not that the system was not functional.

Great news. Thanks!

[charmalu]

I almost always have FULL heat, FULL air, or OFF depending upon the season.[/QUOTE]

same here, full heat when the wheel is in the detent, come out of the detent, and heat disappears.
so run heat on low and leave the rear windows down some.

Charlie

[Skid Row Joe]

Originally Posted by tr1cky

Questions:

What is the proper effect of the auto button?The AUTO button, cancels LOW and HIGH. It has no "in," clicking position.
Is it supposed to click into place?No.

Sounds like you need a new "brain" selector bar. I bought one for my SD when it acted-up as you are describing. It was about $115.00, new from MB dealer 13 years ago or so.

[tr1cky]

Originally Posted by Skid Row Joe

Sounds like you need a new "brain" selector bar. I bought one for my SD when it acted-up as you are describing. It was about $115.00, new from MB dealer 13 years ago or so.

I'm confused. If your answer describes that my unit is functioning properly then why would I need a new "brain" selector bar.

[Skid Row Joe]

Originally Posted by tr1cky

I'm confused. If your answer describes that my unit is functioning properly then why would I need a new "brain" selector bar.

Scratch getting a new one then.

[tr1cky]

Originally Posted by Skid Row Joe

Scratch getting a new one then.

Thanks, I am just making sure that I'm reading it right. Its been a long week and my brain may be a bit mushy.

Thanks for your input.

[leathermang]

I really do not trust the auto system..
is there something pulling ambient air from the passenger area across some sensor in order to start it up ?

[rrgrassi]

Originally Posted by leathermang

I really do not trust the auto system..
is there something pulling ambient air from the passenger area across some sensor in order to start it up ?

On the w123, that little vent in the center of the dash (The famous rotted foam tube is connected to) air is pulled across the air temp sensor by the cabin fan. IIRC, air is pulled by the w126, but it's intake is close to the rear view mirror.

[leathermang]

Does the cabin fan run all the time ? Or all the time the car is running ?

[tr1cky]

Originally Posted by leathermang

Does the cabin fan run all the time ? Or all the time the car is running ?

I will have to check. Unless i hit the O button, i believe i always have air of some type.

[rrgrassi]

Originally Posted by leathermang

Does the cabin fan run all the time ? Or all the time the car is running ?

The fan runs when the any button except the off button is pressed. Auto mode is enabled when the center button or the button between the center and off are pressed in.