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  #1  
Old 10-01-2015, 10:44 AM
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vacuum switch from ac blower to heat blower?

Have been working through some issues with my 1975 w115 300D. The AC fan works (not the ac just the fan) but when I switch off the A/C the heater fan does not work. I tried to get it spinning with a coat hanger through the center vent. No luck. Before I take off the air intake cowl I wanted to make sure the change over switch is working. I read in other posts of a vacuum actuated switch near the accelerator pedal. I can't seem to find it. Any advice or images of what I am looking for under there? Winter is coming!
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Old 10-01-2015, 02:21 PM
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There should be a short shaft above the accelerator on the left-hand side of the central console--this is connected to the changeover switch. Moving it manually through its range of motion should allow you to toggle between the A/C and heater positions--good luck


Tim Kraakevik
kraakevik@voyager.net
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  #3  
Old 10-02-2015, 09:17 AM
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My best guess is that the switch IS working since it turns the AC fan off. But like Tim said, there is a lever that moves in the location he says. The best way to find it is to turn the switch from the AC position to the non-AC position with the car OFF and listen and look at the same time. You should hear it move and you can probably see it. Assuming you don't have a vacuum leak, this should operate a few times with the engine off.

Unfortunately, my understanding is that replacement of the heater fan on a 114/115 is a difficult task.
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Old 10-02-2015, 09:40 AM
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Quote:
Originally Posted by ScooterABC View Post
Unfortunately, my understanding is that replacement of the heater fan on a 114/115 is a difficult task.
not if you have a blowtorch, atom bomb and good luck

Trouble with the switch is it will not hold in the "on" position for the blower fan. Try moving and holding the shaft to see if it activates the fan. Also make sure fuse is good and that you have 12V on both sides of the fuse

let us know what you find
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Old 10-02-2015, 10:16 AM
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Thanks. I have read a lot of posts describing the difficulty/time intensity of replacing the heater fan so I am covering all my bases before I consider tackling that. I will get some time this weekend to see if I can locate a lever that moves when I turn the A/C knob on and off. The A/C fan does stop when I turn the A/C knob off but leave the fan control on so perhaps the switch is working and my heater fan is toast?
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Old 10-02-2015, 03:07 PM
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possible, but do see if you have 12V to the leads. Fuses that look good can be bad, you need to test them
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2011 Porsche Cayman - Bond,James Bond
99 E320 THE Queen Mary
62 220b - Dolly - Finally my Finny!
72 450SL, Pearl-SOLD
16 F350 6.7 Diesel -THOR
07 Lexus RX 350 - Lexi
14 38HP John Deere 3038E Tractor -Mean Green
84 300SD, Benjamin -SOLD
71 220 - W115-Libby ( my first love) -SOLD
73 280 - W114 "Organspende" Rest in Peace
81 380 SL - Rest in Peace
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  #7  
Old 10-08-2015, 03:51 PM
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Had the same problem in the '73 220D. The issue was dirty contacts at the blower fuse on the firewall. That fuse is not located in the main fuse block, but has its own box in the engine compartment. In my car it's located high on the RH side firewall. Could be in a different spot on the 300D. Worth checking out.
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  #8  
Old 10-10-2015, 10:10 AM
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About to tacke this problem soon (actually found earlier post with great pics; love pics, tell a thousand words):

http://www.peachparts.com/shopforum/vintage-mercedes/339223-75-300-how-does-ac-blower-fan-get-switched-picture.html
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Old 10-10-2015, 11:08 AM
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Not to high jack conversation, but on a similar note:

I noticed my center switch (the one that lets in fresh air), doesn't move all the way over. Will only move from left to right and stop dead center (ie, never make it all the way right)?

Could this screw things up (ie A/c to heater); any ideas why it wont go all the way right?

Thanks,

Jub
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Old 10-10-2015, 11:54 AM
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Jub,

Shine a light into the vent and you'll see a a phillips head screw in there, towards the RH side. It's used to adjust the length of the rod that connects the lever to the flap. If you can't move the lever to the right all the way towards the closed position I think you need to shorten the rod by turning the screw in. Experiment with it a little and you will find just the right spot where moving the lever all the way to the right firmly closes the flap.

There are no electric switches associated with that flap/lever. It's just for the fresh air intake through that vent.
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