Help! First the AC and now even the blower motor is out!
 

So this is what happened. I was on a 4 hour drive in my 84 500sel with the AC on the entire time (low fanspeed and medium temp, so I wasn't pushing the climate control system too hard, it was just on the whole time) but somewhere along the way, the AC compressor no longer engaged. The next day, when I turned on the AC, the compressor still wouldn't engage, although the blower still worked. Then, figuring it was the AC relay, I jumped the connection at the relay in the fusebox, and the compressor came on but for only a second; and then all of the climate control system died. Now, the blower motor doesn't even work. I'm thinkin a fuse blew somewhere, but the fuse in the fusebox for the AC and blower motor is intact, so I'm stumped. Is there another fuseholder somewhere along the wiring for the AC and blower motor? And do you know what caused the AC compressor to no longer engage in the first place? What are all the possible problems here?

I have had similar problems with my W126 although a 300SD.

First, the compressor will disengage if the freon level drops past a certain point.

If you did overload the circuit, if, check the wiring at the blower motor.
Take off the right, passenger side under-dash panel and find the wiring harness. Mine got fried once and doing a splice wire cured that particular problem.

I am no mechanic and consider that I am relaying my experience and not tech advise.

L

Well I did hook up a pressure gauge to read the low side pressure and it read greater than 100psi, but I thought that's just because the compressors not on and that's just residual pressure. Is there another reason that the reading is so high?

And I don't think it has to do with the pressure anyway because the compressor kicked on for a second when I jumped the ac relay. It's just that I think a fuse somewhere along the way blew when I did that, or there might have been a short somewhere in the wiring that developed during my four hour drive. What would cause the relay to not engage the compressor in the first place?

But at the moment, I can't get the system running to verify the pressures. Right now, the blower motor won't even turn on, so I'm just wondering where to check (fuses, short in wire, etc) to get the blower motor running again before I tackle the ac problem?

As to the blower motor, check the strip fuse located near the main fusebox next to the first firewall in a small black rectangular case. They like to get a hairline crack right in the middle. They break due to thermally induced metal fatigue.

Also, REPLACE (not just look at) fuses 10 and 11 and the fuse strip tinypanzer mentioned. After this, the system gets complicated. However there is more we can check after we get the basics out of the way. I suggest everyone get a GOOD test light for this kind of work. Check both ends of the fuse holder in question and you will know for sure if it is good or bad. Let us know what you find.

Paul

Ok guys, so this is what I've found. Both the fuses themselves (10 and 11) are good. However, I ran a multimeter test for current, and there is only current going thru fuseholder 10 (the climate control fuse). There is no current at all on fuseholder 11 (the blower motor and ac fuse), so I guess that means a fuse somewhere else along the wiring for the ac/blower motor went out? As for the strip fuse, I don't think my car has one (it's an '84 gray market) and I couldn't find any rectangular box near the fusebox/firewall. Here's a pic of the fusebox area so you can tell me if I just missed the strip fuse, but I'm pretty sure I don't have one.

Sorry for the delay in responding. The strip fuse on my 84 500SEL USA car is forward of the fuse block, just behind the diagnostic connector on the left inner fender. I'm not sure if the gray market cars have one or if the a/c system is the same as the USA version. I do know that there are differences in the USA and EURO versions but don't have any idea what the difference is. I have worked on a 84 280SL euro and the A/C is totally different from a USA 84 380 SL. Maybe pictures of the control panel, compressor, etc may help.

Paul

Ok, I finally got the time to take pics of my climate control system and engine compartment where the strip fuse should presumably be located, although I still can't find it. But here they are, so let me know if you see the strip fuse and what you think the problem might be with my specific climate control system. Also, I discovered another problem that's definitely related to this mess. My horn hasn't worked since the blower motor's been out. Does that narrow down the diagnosis for what the problem is?

On my US car the fuses are on the fender area in your 2nd photo. So look around for small black boxes about the size of a cube relay. There were 2 red fuses in mine that were nasty corroded (had to wire brush the contacts). Changed them a few minutes ago after reading this thread.

I am still trying to get my blower to turn back on, as it has not worked since I purchased this car months ago. :(

This is a step in the right direction. Hopefully you can find your fuses and that solves your issue.

Well I've officially given up looking for the strip fuse that's in the US cars, because I've had no luck spotting it anywhere in my gray market, leading me to assume that my car has no such strip fuse. If anybody happens to see it in the picture I've taken, please let me know, but for now, I'm trying to pinpoint other causes. Does anyone know at what point the horn and blower motor share a circuit/fuse in the wiring? Because as I mentioned, the horn went out along with the blower motor.

Hopefully, when the holiday is over, someone who has more knowledge on this will chime in. There must be fuse protection somewhere (like the US cars), just where the heck is it? :)

That's a good question! Based on the symptoms, I'm assuming the problem lies somewhere in the wiring AFTER the fuseholder for the horn (since there's still current going thru it), and BEFORE the fuseholder for the blower motor/ac (since there's no current going thru that one). If there turns out to be fuse protection hidden somewhere else in the wiring, I would say that the blown fuse is responsible for both the horn and blower motor. So does anyone know of a fuse somewhere along the wiring that supplies power to both the blower motor and horn?

So does anyone know where the horn and blower motor are wired together?

I don't know about the 126, but on the 124 the horn and climate control are on separate fuses. Did you try checking for 12V at the horn terminals? If you don't have the service literature, I highly recommend you get it. It will be invaluable for all your problems. Plus it has the entire electrical diagram.

Yeah they are on different fuses in the fusebox, but I just wanted to know if the horn and blower motor shared wiring at any other point. I'm guessing that when I manually bridged the circuit at the ac relay, I shorted out some wire that supplies power to both the blower motor and horn. So does anyone know the relationship in wiring between the two, anywhere that they share wiring?

So I've been without a blower motor and horn for almost a month... Can somebody please help?

84MB500SEL
I would be happy to help you if I knew ANYTHING about Euro cars. I do know that I once worked on an 84 280SL and the A/C looked like yours and it was an aftermarket add-on. I have looked at the wiring for a car like yours except a US version and the horn and A/C have nothing to do with each other that I could find. The way to fix this type of problem is to take one of the problems (I suggest you start with the horn) and ignore the other. In other words, one thing at the time. When you fix the horn, if the blower still doesn't work, then work on that.
Maybe some of our EURO friends can help if you ask specific questions. For instance, ask "what else is powered by the horn fuse". If you get an answer, then you can check those things to see if they work or not. Let us know the answer and we can give some guidance with those facts.
I just looked and on a US 500SEL Fuse 14 feeds power to the horn switch in the steering wheel. The other side of the horn switch goes to the horns. The other things on Fuse 14 are the cigar lighters, rear window defroster, rear seat heaters and the trunk light. I have no Idea if your car is the same but you can check and see if this information applies to the Euro car.
Sorry I can't be more help.
Paul

On the earlier W123 cars, the strip fuse is mounted inside the evaporator housing at the very top where it connects to the air inlet. I'm wondering since your 500 SEL is a Euro car, if your strip fuse isn't mounted there as well.

FYI: Running your fan at lower speeds will make the AC system work harder. The faster it runs, the more accurate temp indication the temp sensor will receive and thus cycling the compressor more.

Where is the evaporator housing you speak of in the w126?

I mentioned the W123, but the W126 may have the same strip fuse; I don't know. The evaporator housing and fan housing are the same box under the passenger side of the dashboard. In the W123, the fan is mounted just below the right side of the evaporator. The thick wire that connects at the fan motor comes directly from the strip fuse. However, the strip fuse almost never goes bad, hence its out-of-the-way location.

on the 126 cars the strip fuse did not arrive by the factory until 86 with the 420,300 and 560.it was offered as a modification part by benz to basically remove fuse 11 out of fuse box because conns in fuse box would not carry the heavy load and would melt the conns into the fuse box.you will need to undo the screws and lift up the guts of the fuse box and examine the wires leading to fuse 11 to see if they are intact.if they are you will need to trace wiring for hot side of fuse back towards terminal 15 on the ignition switch because one side of that fuse should be alive with the key on.