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post #11 of 25 (permalink) Old 06-25-2014, 10:36 AM
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That unit has a blower as part of the under-dash unit, probably located to the right and back somewhere. So you get nothing when you turn the fan knob, right? On a 108 I'm thinking you have to have the HEATER temp levers to the cold position for the AC to go on - like there is a switch or something built into them to keep the AC from coming on if you have hot air running to the system. So make sure both of the heat temp levers are all the way in the cold (blue) direction. I think that is the lower two levers, towards the center as it appears in your photograph. I don't know if it cars about the position of the other levers, but I would assume that it wants the outside air coming in to be closed also. Which is again, I think towards the center.

I would check all the fuses under the hood - can't tell from the picture but do you have a few small exposed fuse boxes on the passenger side of the firewall? Make sure you are getting power to them. Short of that, I would say to make sure that the unit is grounded by adding a ground wire temporarily and see if the fan starts blowing.

Currently: 1967 250 SL, 1963 220Sb, 1965 300SE Lang, 1971 280SE parts car, 1972 Alfa GTV, 1965 Alfa Duetto, 1993 BMW R100R
Past: 1971 250 C, 1985 300 TD, 1967 250 S, 1968 280 S,1981 300 D, 1982 280CE, 3 Facel Vegas, Borgward Isabella Coupe, Alfa 2600 Sprint, Volvo P1900 (yes), numerous less interesting Volvos, ...
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post #12 of 25 (permalink) Old 06-25-2014, 10:57 AM
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On the W108 (I have a 72), the heater/defrost is completely separate from the AC unit. The AC unit has its own blower located in the passenger side footwell. It is controled by the two knobs on the AC unit (fan and temperature). The unit "maintains" temperature by cycling the compressor based on the temperature out of the evaporator.

Do you know where the loose wire was that your mechanic "fixed"? I would start there. If you are getting nothing (no light/fan/compressor), there are two possible issues; 1) there is a lack of power to the system meaning a fuse and/or wiring issue or 2) the switch that turns on the blower (and consequently the compressor) has failed. The green light tells you there is power to the clutch of the compressor so it will cycle on and off as the compressor cycles.

I have suffered through the failure of this switch. It is no longer available as far as I can tell. It is an infinitely adjustable blower speed switch with a single power input and two outputs. Both outputs are zero volts with the fan turned off. Turning the fan on turns on the blower and also provides power to the clutch circuit. As you continue to turn the blower switch, slide contacts adjust the voltage to the blower motor causing it to speed up/slow down, but the power output to the clutch circuit stays at 12V.

Since I was unable to find a new switch and I hate putting in "new" 42 year old used switches, I replaced mine with a switch meant for a 60s era mustang I believe. It is a 4 position switch so I now have OFF, HIGH, MEDIUM, and LOW for blower speed.

If your fuses are good, I would look at this switch.
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post #13 of 25 (permalink) Old 06-25-2014, 05:45 PM Thread Starter
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All fuses but one tested ok (under hood & in driver side compartment). Replaced that one and the dash lights started working. According to the owners manual, fuses under the hood power ac. They tested fine, but looked rough. I replaced them all, still no luck. Is there a way to test the switch for the ac? I popped of the cover under the ac controls. Here are the pics of that

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post #14 of 25 (permalink) Old 06-25-2014, 05:47 PM Thread Starter
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Here are the pics.

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post #15 of 25 (permalink) Old 06-25-2014, 05:48 PM Thread Starter
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Also, not sure how to ad a ground wire.

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post #16 of 25 (permalink) Old 06-25-2014, 05:52 PM
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Quote:
Originally Posted by KyBill View Post
Also, not sure how to ad a ground wire.
Well since the fan switch is exposed now the ground wire isn't important. Get a test probe, the kind that has an alligator clip on one end of a wire and a test light on the other with a probe and connect the alligator clip to something in the car that is grounded. That would be something metal that isn't painted, or in a Mercedes just about anything with a brown wire running to it. If your car has chrome door jam light switches, connecting the clip to that would be OK, or to something that is bare metal. Then (with the car turned on so that power should be running to the switch) touch the probe to each of the terminals on the switch. With the switch off you should get power going to one of the terminals. With the switch on you should be getting power going to more than one of the terminals.

Currently: 1967 250 SL, 1963 220Sb, 1965 300SE Lang, 1971 280SE parts car, 1972 Alfa GTV, 1965 Alfa Duetto, 1993 BMW R100R
Past: 1971 250 C, 1985 300 TD, 1967 250 S, 1968 280 S,1981 300 D, 1982 280CE, 3 Facel Vegas, Borgward Isabella Coupe, Alfa 2600 Sprint, Volvo P1900 (yes), numerous less interesting Volvos, ...
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post #17 of 25 (permalink) Old 06-26-2014, 05:07 PM Thread Starter
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Switch off, I get power to one terminal. Switch on, still only power to one. If I turn it all the way, the light goes out on the tester for that terminal. Does this mean the switch is bad?

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post #18 of 25 (permalink) Old 06-26-2014, 09:12 PM
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If I remember correct, power comes in the center spade (looks to be orange from your photo). If you have power here but nothing on the other two ever, then my guess is switch is bad. You can test by jumping the hot to the other two with a piece of wire. One should turn on the fan and one should turn on the green light and energize the clutch (as long as temp is on cold setting).

When mine failed, I tried in vain to find a new one. I ended up with a straight 3 speed switch. I believe mine is from Nostalgic Air, part number 119-9910.

Mine is now off, low, medium, high. It has a clutch contact as well. $20 and it was plug n play.
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post #19 of 25 (permalink) Old 06-26-2014, 09:33 PM Thread Starter
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Thanks! I'll try a new switch. I didn't see the part number you listed on their site. Does this look like the part?

http://nostalgicac.com/binary-high-l...e-threads.html

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post #20 of 25 (permalink) Old 06-27-2014, 06:49 AM
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No. On their site, go to controls and motors; then ac blower switches; then it should be the resistor blower fan switch
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