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  #1  
Old 06-24-2022, 10:43 PM
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1982 W123 aux fan wiring diagnosis

1982 300CD I jumped the fan with jumper cables and the fan works perfectly. So, It's not getting power to the fan. I can notice that the A/C doesn't work well when it's hot outside and I'm in traffic. Are there any good wiring diagrams?

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  #2  
Old 06-24-2022, 11:32 PM
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The electric fan on a W123 car is wired through the air conditioner pressure switch which is located in the AC hose near the receiver drier. You may have a bad pressure switch or your AC system may be low on freon. With the AC on high look at the sight glass on top of the receiver drier. If you see bubbles that is an indication of low freon. The pressure switch will prevent the AC compressor from engaging or the fan from coming on if low on freon. This may also explain why your AC does not work well in hot weather.
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Old 06-25-2022, 10:49 AM
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Originally Posted by BWhitmore View Post
The electric fan on a W123 car is wired through the air conditioner pressure switch which is located in the AC hose near the receiver drier.
No, it isn't. The pressure switch is applicable to the compressor clutch. The aux fan relay is powered through a temperature switch on the receiver/drier.
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Old 06-25-2022, 11:06 AM
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Originally Posted by BWhitmore View Post
The electric fan on a W123 car is wired through the air conditioner pressure switch which is located in the AC hose near the receiver drier. You may have a bad pressure switch or your AC system may be low on freon. With the AC on high look at the sight glass on top of the receiver drier. If you see bubbles that is an indication of low freon. The pressure switch will prevent the AC compressor from engaging or the fan from coming on if low on freon. This may also explain why your AC does not work well in hot weather.
There is plenty of "freon". It's ice cold when it isn't scorching hot out side and I don't see any bubble through the little glass. (Rather hard to see anyway) I've also jumped the sensor and the fan doesn't turn on.
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Old 06-25-2022, 11:21 AM
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Originally Posted by gregp1962 View Post
I've also jumped the sensor and the fan doesn't turn on.
Are you 100% sure you jumped the correct sensor? Was it the one with two spade terminals?
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Old 06-25-2022, 11:53 AM
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I'm pretty sure I jumped the correct one. Although the jumper isn't installed in this picture. You can see which ones I jumped.

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Old 06-25-2022, 12:12 PM
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Originally Posted by gregp1962 View Post
I'm pretty sure I jumped the correct one. Although the jumper isn't installed in this picture. You can see which ones I jumped.

That's the one. Assuming the key was in the RUN position, the next thing to check would be the fan relay on the top of left fender well.
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Old 06-25-2022, 02:23 PM
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Originally Posted by tangofox007 View Post
That's the one. Assuming the key was in the RUN position, the next thing to check would be the fan relay on the top of left fender well.
The key was in the on position with the engine running and A/C on.
I did switch relays. The A/C still works ok. Just no Aux fan.

I also tested the power input into the temp sensor. There is power there. You can't see it in the picture. But, the test light was extremely dim. Maybe I should have tested voltage there.

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Old 06-25-2022, 06:08 PM
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With the RD temp switch leads jumped, and everything running as before, check for current at the pigtail connector to the aux fan. These connectors, being so close to the ground, tend to suffer from bad connections from all the road crud they are exposed to.
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Old 06-27-2022, 11:10 AM
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Originally Posted by 280EZRider View Post
With the RD temp switch leads jumped, and everything running as before, check for current at the pigtail connector to the aux fan. These connectors, being so close to the ground, tend to suffer from bad connections from all the road crud they are exposed to.
There's no current with the leads jumped, (Or properly connected) There is no current at the fan connection. Is there a good way to jump the relay to check that?
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Old 06-27-2022, 08:52 PM
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Sorry, I don't have the pin numbers for your car's aux fan relay, however, on many 123 cars, pins 30 and 87a are the pins you would jump for current to the aux fan. You should verify that these are in fact the correct pins for your car.
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  #12  
Old 06-28-2022, 04:37 PM
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Does anyone have a wiring diagram for at least the Aux fan section?
1982 300CD US
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  #13  
Old 06-30-2022, 01:39 PM
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I'm just going to add a relay triggered by the switch at the dryer. Does anyone know how many amps these OEM fans draw?
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  #14  
Old 06-30-2022, 02:23 PM
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Originally Posted by gregp1962 View Post
I'm just going to add a relay triggered by the switch at the dryer. Does anyone know how many amps these OEM fans draw?
To be on the safe side, use the amperage of your car's fuse for the aux fan.
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Old 06-30-2022, 03:20 PM
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Originally Posted by 280EZRider View Post
To be on the safe side, use the amperage of your car's fuse for the aux fan.
Good thinking. Also, I'm planning on using 12 ga wire. I think that should be enough for the Aux fan. 12 ga supposedly can easily carry 20 amps at 12v. 10 ga looks way to big. Surely this OEM fan doesn't use over 20 amps

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