1998 C230 Aux Fan doesn't come on
 

I have a 1998 C230 with the non-supercharged motor. A/C blows warm, compressor does not kick on. The auxiliary fan never comes on, regardless if I'm using the air conditioning or not. The engine temperature stays right around 80 Celsius unless I sit in traffic, in which case it will head up towards 100 and the auxiliary fan does not come on.

Haven't found any bad fuses or relays, the connection to the fan is in good shape. The a/c system is full of r-134a. I'm tempted to just replace the fan, but I don't have much diagnostic information on this vehicle so I don't want to jump to a conclusion.

Not an expert on your C230 but the Aux Fans are normally set to come on around 105C without the A/C on.

If the A/C is on, and the pressure is below 15 bar (220 psi), the Aux Fans will stay off.

Check the "blue" colored table (about center of page) here. It shows the temperature and pressure interrelationship.

I was thinking the logic of the aux fan was that it needed to come on before the a/c compressor kicked on.

In the heat of the summer, sitting in traffic, the temperature gauge appears to read above 100 degrees Celsius at times. The only way the temperature would go back down is if I turned on the heat or started moving again.

No. . either PRESSURE or TEMPERATURE can turn the Aux Fans on . .

MB specs it at "100C" . . but practically, it's more like 105 - 106C.

The AC control unit can be put into diagnostic mode to read out sensor values for troubleshooting. Here is one thread, and you can find others by searching:

W210 Air Conditioning Diagnosis | EClassBenz.com

Hopefully you can find the trouble this way. Good luck.

OK, thank you for your help! I will see what I can figure out with this information.