The aux fan on the front of the radiator on my 85' 300D is not comming on. I cannot honeslty remember if it only comes on when the AC is on or if it reaches a certain temp. I have replaced the fuse, just to make sure it was good. I have also hooked up the mulitmeter to the plug under the radiator and it is getting juice. The AC has a leak and has not been used in some while so I cant determine if the fan itself is dead or it isnt comming on for a reason.

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1980 300D European
"The Red Fox"
200,000 miles

2003 Chevrolet Silverado

609 Certification

Only when the temperature of the Reciever/Dryer is over 60? 80? 'C, unless the temperature sensor on the dryer has been bypased, if it has been bypassed, then whenever the A/C is turned on the Aux fan will operate.

If the a/c refrigerant level is low, the fan will not come on, as the temp will not each the required 62 degrees C.

I believe that the refrigerant is completely gone. About 2 years ago I have the AC system checked and the refrigerant replaced but after about 6 months it lost the cool and to keep the compressor in good shape, I havent used the AC. I am switch to the newer coolant in a week or two and hope that the AC equipment is in good shape. I was just concered as I know there is a 20% rise in heat when the AC is on and I wanted to make sure the aux. fan was working to take care of some of the heat.

Any suggestings or concerns from switching to the R-12 to the R134a?

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1980 300D European
"The Red Fox"
200,000 miles

2003 Chevrolet Silverado

609 Certification

Don't even think about it!!!

So am I better fixing the leak and keeping the R-12 system? As opposed to converting? What are the problems with converting?

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1980 300D European
"The Red Fox"
200,000 miles

2003 Chevrolet Silverado

609 Certification

R-134a will not provide adequate cooling in the W123.

Well being in Texas, where AC is a must, I will take that in to account very much so. Thank you for the heads up.

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1980 300D European
"The Red Fox"
200,000 miles

2003 Chevrolet Silverado

609 Certification

If your getting a good ground and positive from that plug, then the brushes may be bad in the fan. However, you shouldn't have power there unless the engine is over a certain temp, or as others have stated, the freon is over a certain temp/pressure. Back to the fan, with power to it, try pushing in on the center of it with a screwdriver or piece of wood. If it starts working, chances are it's the brushes.

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85 300CD
83 300TD
78 240D (daughter)