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  #1  
Old 06-21-2010, 08:33 PM
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Exclamation 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?

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  #2  
Old 06-21-2010, 10:03 PM
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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
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  #3  
Old 06-22-2010, 11:05 AM
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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?
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Old 06-23-2010, 03:08 PM
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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?
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Old 06-23-2010, 04:52 PM
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Quote:
Originally Posted by LarryBible View Post
The first step in this troubleshooting process, is to connect MANIFOLD gauges and verify refrigerant charge.

You will have to monitor BOTH high and low charge while system is running.

If you have 100 low static pressure the low pressure switch should be activated. Use an ohmmeter across the switch to confirm. If it is made and the compressor is still not on, measure voltage at switch. If there is none, go back to the CCU and check for power to it.
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?
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  #6  
Old 06-23-2010, 05:39 PM
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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.
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  #7  
Old 06-23-2010, 06:28 PM
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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.

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Old 06-24-2010, 04:08 PM
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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.
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Help! First the AC and now even the blower motor is out!-benz-fusebox.jpg  
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  #9  
Old 06-26-2010, 08:56 AM
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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
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  #10  
Old 07-02-2010, 04:38 PM
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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?
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Help! First the AC and now even the blower motor is out!-image1.jpg   Help! First the AC and now even the blower motor is out!-photo.jpg  
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  #11  
Old 07-02-2010, 11:03 PM
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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.
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  #12  
Old 07-04-2010, 07:56 PM
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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.
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  #13  
Old 07-04-2010, 08:23 PM
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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?
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  #14  
Old 07-09-2010, 06:12 PM
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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?
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  #15  
Old 07-11-2010, 06:57 PM
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So does anyone know where the horn and blower motor are wired together?

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