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Auxiliary Fan(s) Not functioning

2945 Views 64 Replies 5 Participants Last post by  Kevin G.
This if my first post so bear with me. I've reviewed the threads on this issue and am still quite confused. First some background

The Car:
W124 1993 300E
235,000 Miles
Well maintained, though not perfectly
Burns a little oil, radiator probably needs replacing, recent inspection shows most everything in working order.

I have the desire to keep this car going as long as possible, so I want to identify what needs replacing and take care of it. I am familiar with these models, as I have had 5 previous to this. I still don't know every bit and piece but I know enough to be dangerous.

The Issue:

I recently had a son, and this is our only car in Washington DC. It has been hotter than the blazes of hell recently and so Air Conditioning has been a must. I never much bothered with it before as I just used window A/C as it were. But since having the kid, it needs to work. It never really blew cold, but I could do a weird hack. If I shut down the car, when I restarted it, the AC would blow cold, for a bout 10 mins or less, then go hot again.

I checked the pressure in the AC system and it was way too high. I got it back down to legitimate levels and it would blow cold air for longer for about a day. I have noticed that the car would get quite hot quite fast, and when it would get hot, the Aux fan would kick in, the AC would blow cold and the temp would go down.

After a drive today with the same intermittent AC and hot as hell outside temp, I decided to check out the whole system. I am pretty sure that when the AC is turned on the aux fan is supposed to turn on and cool the engine, and perhaps also help it blow colder. When I turned on the AC the aux fan didn't go at all.

Testing the Aux Fan

Here is the test I did.

1) With the key ON I pulled the wire on the temp sensor. The first time I did this, the passenger side fan started right up, but the driver's side didn't, as it did when the motor got hot.
2) With the key ON and the Plug OFF the temp sensor, I pulled the plug for the fans to check the connections, the left fan shut off, the connections were clear and tight, and it started up when I put it back together.
3) Put the plug back ON the temp sensor and turned the key OFF.

This seemed to confirm the aux fan would turn on, but perhaps the drivers side needed to be replaced. I wanted to use a voltimeter to check the power at the connections.

1) With the key ON I pulled the plug off the Temp sensor - fan did not engage
2) Checked the volts at the fan plugs, not juice
3) Bridged the temp sensor plug, no volts at fan connector

This indicated that the fans had just stopped working, perhaps the relay?

1) Open the relay box, pull the Relays (A,B I believe), clean the connectors, use compressed air to blow out the plugs, and put them back in,
2) Key ON, temp sensor plug OFF - no fans, no volts at the connector
3) When I pull the temp sensor plug i cant hear a pop in the relay box coming from the D relay. Remove the D relay and no pop.

Conclusion

I am confused. This all seems to suggest a relay, right? Can I bypass the relay to see if the fans turn?

Looking for suggestions.

Update: Connected the connector to the fans directly to the battery and they didn't turn on. Pulled the plug on the temp sensor with key ON and checked the female connector side, showing 12v. This seems to indicate that it is the Aux fans that are bad.
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That is the goal. I also replaced the B relay with the new one and it seemed to work. I'll let you know what happens.
I changed it all out and still nothing. I am guessing the resistor is bad. When I put power directly to the low power side, the fans go. Could it be the relay?

Hope my article can help you have a better idea of the activation circuit.
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Part of me just wants to bridge the resistor, knowing that it will mean full fans when AC is on. Still. I cannot find that resistor available anywhere.
Part of me just wants to bridge the resistor, knowing that it will mean full fans when AC is on. Still. I cannot find that resistor available anywhere.
Junk yard has it
Been looking all around the area and even contacted MBIparts. I did find this one, and though not perfect, It seems like it will work.
Been looking all around the area and even contacted MBIparts. I did find this one, and though not perfect, It seems like it will work.
Can anyone give me advice on something my A/C is doing on a 1994 W124 E320. I have had the blower fan and regulator replaced along with the clutch adjusted. It will be cooling
fine, and when I get back into the car it will not work. The next morning or that afternoon, I get in it and it is cooling again. But sometimes it does it in the middle of a long
day of 100 degrees when I am out shopping. Any ideas?

Thanks.
So based on this post, I ran a wire from the battery to the resistor. The low speed ran fine so my resistor is good.

So I took a paperclip and bridged the drier sensor and they didn't fire up at all. So that makes me think it's the relay.

Agree?
Just did and still nothing. Confirmed that the B relay is for the high fans and the C for the low. Pulled the B out (which is the purple one I bought with the fuse in top) and the fans don't run when I pulled the temp sensor plug. When I switched the two, the fans ran when the temp plug was out but not when the AC is on.

The mystery continues. I'll post another video soon showing everything.
A/c pressures look good. Look at the red sensor on the drier. Bridge that sensor with the paper clip and let me know of the fans come on

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Can anyone give me advice on something my A/C is doing on a 1994 W124 E320. I have had the blower fan and regulator replaced along with the clutch adjusted. It will be cooling
fine, and when I get back into the car it will not work. The next morning or that afternoon, I get in it and it is cooling again. But sometimes it does it in the middle of a long
day of 100 degrees when I am out shopping. Any ideas?

Thanks.
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A/c pressures look good. Look at the red sensor on the drier. Bridge that sensor with the paper clip and let me know of the fans come on
Isn't it operating as intended?
Isn't it operating as intended?
It may not if your fans aren't coming on
It may not if your fans aren't coming on
In the video the fans did come on!
In the video the fans did come on!
I saw, so your concerns are resolved? The fans wont come on the second the a/c system turns on, the presure in the system has to build, then theyll come on. Could have been that your system was just low, or that red sensor you never tested is working intermitenetly, good luck.
Yeah, I get that it should turn on when the AC is on, and not just when the pressure gets high. That said, my main goal is cold AC, and it seems to be giving me that. I will test it today and see if it works, since it is near 100 F in DC.
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