'71 220D What is this knob for? (photo)

What is the left knob above the radio for?



It seems to be broken since the "D" shaped rod doesn't connect with the knob.

The middle knob is for the lighter and the right one is the 4 way flasher. The defroster switch is down below the radio. Also, the knob labeled Defrost turns on the A/C compressor and fan. Why is it labeled Defrost? Is there a switch just to turn on the fan for heating without A/C? What is the position of the 4 levers for max A/C cooling?

[JimSmith]

atikovi,

Your levers for heat and air flow direction are a little off. The icon with the layout for the defrost mode should have the heat on full, which has the two heater levers in their outward position, and all the air going to the windshield, so one lever is all the way outboard (the one with the arrow pointing upward) and the other all the way inward (the one that directs air flow to the footwell, which minimizes flow in that direction). It looks like your heat and flow direction knobs on the levers have been reversed.

The round knob between the levers with the word defrost on it is the fan control. The fan must be atleast in the first speed to turn the compressor on. Otherwise it is probable the air cooler will freeze up and no air will come in.

The knob you have that is broken is the airconditioning temperature selector knob. The rule for all these symbols is you move the control in the direction of the icon feature getting thicker to get more of that feature and in the direction to get less. In the case of the defrost knob, the intent is that the defrost position is at the end of the full thickness of the blue curly icon. Meaning when you turn it all the way the fan is on all the way and presumably you would only do that to make the windows defrost.

The airconditioning temperature selector knob runs the same way, as you need more cooling you turn it in the direction that makes the icon symbol a thicker blue curly shape.

I would think you can dope out if someone took the heating and flow direction knobs off by turning the fan on and fiddling with the flow direction (blue lever knobs with arrows at the thick ends pointing up or down) and heat levers to see which ones make the air go up on the windshield. Once you get these straightened out you should be able to maximize cooling by shutting the heat off all the way, and turning the air conditioning all the way up when you replace the knob that is broken off.

Hope this helps, Jim

[dabenz]

JimSmith has it about right.

The following is from the air conditioning system manual (115 834 01 00): “For cooling the combination temperature vacuum switch must be moved from the lefthand stop to the right (this is your broken knob). Moreover, the blower switch (between the sliders like JimSmith said) must be switched on.”

Next is my paraphrasing:
The top sliders are the air volume control levers. Right one out gets air to your feet. Left one out puts air to the defroster vents. To the middle closes them.

The bottom sliders control the heat for the left and right sides of the car. In is cold, out is hot. The cartoon beneath the word 'DEF' shows how to get all the hot air to the defroster vents. At highway speeds you don't need the blower running to get heat, but remember that you do to get A/C. Somebody put the slider knobs on wrong: the red ones should be on the bottom (red for heat, blue for air). The fifth slider (above the center vents) gives extra air (unheated) through the dashboard vents. To the right is off. For me, figuring out that fifth slider and adjusting the heater valve cables was the difference between keeping daBenz stock or putting in the A/C from the parts car.

The combination temperature vacuum switch may be expensive as it controls both A/C temperature and the vacuum operated flappers that route air past the blower. Electrical connector at the back of the assembly. Getting there is the hard part, and I can't remember if there's a support box behind the radio or room behind the air intake next to the foot throttle or room to work a hand and a mirror under the dash. Otherwise you'll have to pull the console (the bottom bolt is under the center intake panel). Also, once you replace or repair that temperature switch, it is adjustable so you don't ice the evaporator.

I like your radio. Mine (1970 220D) is a BC/FM radio.


Good Luck,
daBenz

[Fisherman]

You probably already figured this stuff out but I just fixed mine so thought I would throw in my limited MBZ knowledge.
The knob is in fact the air conditoner control knob and acts as both a temp selector and at the very far left side of travel a vacuum switch. The not so funny thing is that the knob is actually threaded onto the shaft that has the cutout in it.
So go figure, when you have to turn it off all the way to the left to get the vacuum switch to allow the vacuum actuators to close the vents so that you have heat the know turns on the end of the shaft.
Even better, the vacuum switch is tough to turn so I was driving around in 20 degree weather with the airconditioner on and wondering why it was so damned cold.

Anyway, I opened the center console (didn't know aboutt he little screw through the bottom vent and broke the mount there) and removed the fascia mounting nut from the front of the switch then manually turned the "shaft" counter clockwise until I heard the vacuum actuators throw over the vents. Then I pulled the shaft and knob as you have in your picture. Unscrewed the know from the shaft and applied a small quantity of (you guessed it already?) JB Weld to the threads on the shaft. Screw the knob back onto the shaft. Went to the car and fit the notch on the shaft into the switch and then did a little fine tuning to get the arrows lined up in the "Off" position.
All is now as it should be and I have heat on cold mornings and air conditioning in the afternoon.

Good luck and I hope I made sense.