Fan is probably blowing a fuse because there is a shortage in the wiring somewhere. Check the wires first. Visually inspect them for wear. As fas as one fan not at full speed....the fans have 2 speeds: high and low. It will only reach full speed if the temperature of the car reaches about 105*C. To test that the high speed fan is working, unplug the coolant temp sensor located on the engine block top driver side, should be a blue two prong plug "on" the aluminum part of the engine block

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1990 190E 3.0L