The A/C unit, which had been working great, all of the sudden quit. No blower, no compressor engage no nothing. The older factory A/C's were integrated under the dash, similar to the dealer installed models, with two knobs, one for fan speed the other for temp. Checked all fuses, replaced the #5 for good measure, since one of the items it is dedicated to is "valve unit and compressed air" (but I'm betting that is for 300's). Still no go.

Is there another fuse, perhaps under the hood for the A/C unit? Could it be that the on/off speed control switch has gone south? I did pull the access plate from under the dash, and can see the backside of the switch. It appears to have a fairly large ceramic body, with the wiring attached with screws/small bolts. I will be attempting to remove the switch in the next day or two to try and check for continuity (or lack of) in all positions. Any Ideas?

I did fail to mentions that once earlier last week, the A/C shut down as I backed out of the garage, and simply cycling the unit on/off got it working again. But that doesn't work now.

TIA

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Mike Tangas
73 280 SEL 4.5

There are no fuses in the fuse box that apply to the A/C. The A/C fuses are in one of the small "2 fuse" fuse boxes on the firewall.

The power for both the blower and the compressor are engaged by the blower switch and it is prone to failure. I'd bet on a fuse though.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

Thanks Steve, I'll try to locate the 2 fuse, fuseboxes to check them out.

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Mike Tangas
73 280 SEL 4.5

Steve,

That didn't take long, I located the fuseboxes, there are four of them. You were correct, the fuse was blown. Well, more than blown, it suffered serious meltdown, even melted the cover a little bit.

In checking the fuseboxes, I noticed that the two closest to the fender had red (25amp?) fuses, when I got to the third it had a red and a white fuse. The white fuse was the problem. Replaced with two new red fuses, and the system is working great.

This leads to a couple new questions. The box closest to the fender held 2 red, the next box only has one red, but 2 fuse holders, is it supposed to have 2 fuses? Should all the fuses be the red fuses, or should they be of different amps? And last, the fourth box, the cover is held in place by a knob, only has one white fuse. What does this fuse power, if you have any idea, and should it be white or should it also be red?

Once again, thanks for the valueable assistance provided by this website!

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Mike Tangas
73 280 SEL 4.5

The one with the knob was usually the radio fuse. A white (8amp) is suitable here. Many of the fuses were red because they powered motors (16amp). They power the window motors, the blower motor, and possibly the aux cooling fan.

All the wiring will take 16amps so I wouldn't worry. These fuses often corrode because they are sorta outdoors so to speak. The corrosion causes poor contact (high resistance) which causes the heat that melts them down. A short circuit takes out the fuse first.

BTW the 25amp fuses are blue.

The one with the knob was usually the radio fuse. A white (8amp) is suitable here. Many of the fuses were red because they powered motors (16amp). They power the window motors, the blower motor, and possibly the aux cooling fan.

All the wiring will take 16amps so I wouldn't worry. These fuses often corrode because they are sorta outdoors so to speak. The corrosion causes poor contact (high resistance) which causes the heat that melts them down. A short circuit takes out the fuse first.

BTW the 25amp fuses are blue.