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  #1  
Old 07-05-2011, 07:39 PM
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Location: Pennsylvania
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AC Compressor Won't Engage

Since last summer, for my 1984 500SEL, the AC no longer works and I am lost on what to check. When I press the AC switch, none of the AC components engage. I checked for current at the compressor and there's none when the AC is switched on, although the switch itself lights up. All fuses are good and I believe the relay itself is good as well. The AC hasn't worked ever since I ran it for 5 hours straight on a long drive, so maybe it's a burnt wire? What should I check first and how should I approach tracing the wiring down to the problem?

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Old 07-06-2011, 08:40 AM
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Does the blower motor work? Have you checked fuses 10 & 11?
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  #3  
Old 07-06-2011, 09:29 AM
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Go to the top of the page in the diesel forum... and read the sticky on MB AC.
That will give you some ideas and perhaps good questions..
Your assumption as to wires , with nothing smoking, and no fuses blown is not logical.
First you jump the low pressure switch on the Rec/drier to see if that is what has cut off electricity to the compressor TO SAVE IT from running without lubrication due to low refrigerant...

only jump it a few seconds....

then you are going to need to put gauges on the system and report the results...
but very specific criteria to get good pressures test results are needed... those are included in the Sticky at top of page.
Report back to here the results of jumping the low pressure cutout switch...
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Old 07-06-2011, 09:40 AM
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I'd bet some $$ the charge is low. Are you still 12 or converted to 134?

Pressures will be key

Jonathan
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Old 07-06-2011, 03:39 PM
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Quote:
Originally Posted by mbdoc View Post
Does the blower motor work? Have you checked fuses 10 & 11?
Yes, the blower motor is operational. However, when I jumped the connection at the AC relay, the compressor came on for a second but then went out and blew the blower motor fuse along with it. I've replaced that fuse since, and now the blower motor works again, although the compressor still doesn't come on.
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Old 07-06-2011, 03:46 PM
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Originally Posted by jhodg5ck View Post
I'd bet some $$ the charge is low. Are you still 12 or converted to 134?

Pressures will be key

Jonathan
I'm converted to 134, but how should I measure the pressures when the compressor won't engage?

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