Question about 1987 Mercedes-Benz S-Class

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We keep burning up a/c relays in our 1987 Mercedes Benz 560 SEL, what may cause this problem?

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  • uno_1 May 26, 2010

    have you checked for a short or a bad ground...?



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There are several possibilities and you should have a wiring diagram if the problem is not moisture. Some manufacturers put the relays on the firewall or the area beneath the A/C pipes. There are several parts on the A/C that sweat while working.

The water gets into the relays and shorts them out. Because the relays can link to other wiring and the mounting holes are in the same place, the mechanic reinstalls the new part in the same bad place. You should look under the hood for the relays and note water and rust in the area.

If you are not the original owner, someone may have used the same relay twice and overloaded the relay by bypassing another bad relay. This is why you would benefit from a color coded wiring chart.

It is also possible that the Voltage Regulator is bad and letting too much juice in the entire car system. The same relay just happens to be overloaded and as the weakest link, it continually fails. Autozone and Oreillys can scope your car for free and let you know what the Voltage Regulator is doing.

Posted on May 26, 2010


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