Hi everyone...

In my 1990 230E the Aux fan does not come on, .. even when i turn on the AC. There are 2 (black) relays on the driver side of the engine compartment firewall. Could one of the relays be the problem. While driving the temp goes to 110!. A week back the fan was working and the max temp was around 100!. How do i diagnose the fan?.

Help is appreciated.

Start by jumping the plug terminals at the coolant sensor on the head (usually green or blue). If the fan comes on, the fan is working (obviously), and the problem is clearly on the 'A/C kickin' side of the equation.

If the fan does not start, try providing 12volts directly to the fan motor to see if it turns.

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1986 300E 5-Speed 240k mi.

You might try checking fuses too.