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1976 280
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Discussion Starter #1 (Edited)
LAST thing to correct and this car will be 100% correct and functional. My 'guy' has converted the A/C and verified that it blows/works cold, one issue: cannot determine where the vacuum source is for the vacuum connections from the A/C thermostat-switch to the change-over switch 'gets' it's vacuum. We figured it must be a line coming through the firewall, but cannot determine which or where.

The portion of the switch/thermostat in question is highlighted in my (amateur) effort below:

2608132


Any help much appreciated.

Regards,

DWConnell
 

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'72 250C, '74 280C, '85 500SEL, '81 300CD.
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Hoo boy, this can be a can of worms. 99.9% of the A/C units are stateside factory add-on's following (for the most part) Daimler Benz guidelines.

The source for the vacuum control you are showing is USUALLY a "tee" connected to either the intake manifold or leading from the vacuum reservoir line. The actual connection points can vary depending on the installer.

The switch supplies the "change-over" valve, located on the side of the lower console above the accelerator linkage, and the fresh air/recirculating flap mounted in the center console.
 

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1976 280
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46 Posts
Discussion Starter #3 (Edited)
Hoo boy, this can be a can of worms. 99.9% of the A/C units are stateside factory add-on's following (for the most part) Daimler Benz guidelines.

The source for the vacuum control you are showing is USUALLY a "tee" connected to either the intake manifold or leading from the vacuum reservoir line. The actual connection points can vary depending on the installer.

The switch supplies the "change-over" valve, located on the side of the lower console above the accelerator linkage, and the fresh air/recirculating flap mounted in the center console.
Excellent response, thanks. We have a clue here, in that the system worked when I got the car... LONG (heart-warming) story, I am the second owner. So, we (my 'Guy' and I) recently got the door locks and cruise control working. OK, HE got it working after I had worked on it. So what we know is that in my diagnosis of the systems first.. I probably caused this by disconnecting something. So, seems to me there should one line coming through the firewall that we need to identify or locate (since it was working...). And then there should be two disconnected lines under the dash leading to dampers.

I think what we need is to know which vacuum port is which on this switch

Sound reasonable?
 

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'72 250C, '74 280C, '85 500SEL, '81 300CD.
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982 Posts
I don't have my coupe here so I can't check which line goes where. Sorry.

I don't know how familiar you are with the W114 climate systems but there a couple of things you should know.
The heat/defrost fan is a separate unit from the A/C blower fan. Default for the system is the A/C blower fan which is the "squirrel cage" blower located in the center console. The heat fan is located on the transmission tunnel.

Fan control speeds are operated by the rotary switch which is located in the center of the dash. The changeover micro-switch, operated by a vacuum diaphragm, selects which fan is activated. Fan speeds are controlled by varying the resistance of the earth/ground connection by way of a resistance unit located beneath the fresh air cowling.

Time to break out the Mityvac. Shouldn't be too hard to figure out. Famous last words, ehh?
 

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Yup, that'd do it. The relevant pages you want are the last two frames of the PDF file.
 
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