A/C help, condensor fan not turning - Mercedes-Benz Forum
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#1 (permalink) Old 06-23-2013, 08:07 PM
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A/C help, condensor fan not turning

Noticed the vent temp wasn't as cold as it should be now that the temp is rising, added some R12 and the fan on the front doesn't kick in when the compressor is turning. The A/C didn't seem to get very cold until after I finished filling it and drove it at highway speeds. Is there a relay for the fan that kicks on at certain temps or is it set to engage when the a/c is engaged?

1981 240D---234K - They said she was too far gone to be brought back ......... she lives!!! http://www.benzworld.org/forums/w123...completed.html
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#2 (permalink) Old 06-23-2013, 09:27 PM
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It's activated by a pressure switch on the a/c drier. You'll need to excavate the system if you want to replace the switch.

Alternatively, and this is what I did, is to connect a relay to the fan (have you actually checked that the fan is working?) which is activated by the compressor's wire.


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#3 (permalink) Old 06-23-2013, 09:43 PM
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I haven't really had a chance to check the integrity of the fan yet frans, I just noticed it wasn't turning when filling it with R12, is there a quick way to short a relay to check it?

1981 240D---234K - They said she was too far gone to be brought back ......... she lives!!! http://www.benzworld.org/forums/w123...completed.html
1983 300TD--103K
1995 E300D--162K
Yea these cars will last a million miles but what with terrorists, natural disasters and the H1N1 swine flu pandemic... God help us there's anyone left here to drive them.
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#4 (permalink) Old 06-23-2013, 09:49 PM
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Just unplug the fan from the main wiring harness and connect it with a few feet of wire to the battery. My bet is a faulty fan; not the pressure switch.


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#5 (permalink) Old 06-23-2013, 10:28 PM
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I hope it IS the fan frans as I have my daughters 81 in my garage waiting to be salvaged and it had working A/C so I could easily swap out.

What size of relay did you use in case I have a pressure switch issue?

1981 240D---234K - They said she was too far gone to be brought back ......... she lives!!! http://www.benzworld.org/forums/w123...completed.html
1983 300TD--103K
1995 E300D--162K
Yea these cars will last a million miles but what with terrorists, natural disasters and the H1N1 swine flu pandemic... God help us there's anyone left here to drive them.

Last edited by Cyberbach; 06-23-2013 at 10:30 PM.
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#6 (permalink) Old 06-23-2013, 10:39 PM
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Just a regular 30 Amp SPDT (5-pin) relay - shouldn't cost more than three bucks, or so.


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#7 (permalink) Old 06-23-2013, 10:59 PM
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cool, didn't know to go with a double or single throw, I usually err on the double throw and 30 amp sure seems safe enough. Thanks again frans.

1981 240D---234K - They said she was too far gone to be brought back ......... she lives!!! http://www.benzworld.org/forums/w123...completed.html
1983 300TD--103K
1995 E300D--162K
Yea these cars will last a million miles but what with terrorists, natural disasters and the H1N1 swine flu pandemic... God help us there's anyone left here to drive them.
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#8 (permalink) Old 06-24-2013, 05:36 AM
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I thought the fan only came on at a certain temperature. At least that is my experience with the system. The relay for the fan is right next to the relay for the compressor.
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#9 (permalink) Old 06-24-2013, 08:54 AM
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Originally Posted by ichris93 View Post
I thought the fan only came on at a certain temperature. At least that is my experience with the system. The relay for the fan is right next to the relay for the compressor.
Seeing as the fan is pressure-switch activated, I doubt temperature has anything to do with it.

If the fan checks out with direct 12 volts, I think you may want to check out the fan's relay before excavating the system to replace the pressure switch.


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#10 (permalink) Old 06-24-2013, 09:11 AM
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Originally Posted by frans-c View Post
Seeing as the fan is pressure-switch activated, I doubt temperature has anything to do with it.

If the fan checks out with direct 12 volts, I think you may want to check out the fan's relay before excavating the system to replace the pressure switch.
On a 1982 240D, which is what I have, the aux fan temperature controlled. At 144F it comes on. A/C help, condensor fan not turning-imageuploadedbyag-free1372090158.252265.jpg



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You're kind of a compromise. You drive, you break down, then you take it apart.
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