I have a '95 E320. I have replaced the thermostat, citrus flushed and refilled with MB coolant and replaced the mono valve. Now I have heat, but the AUTO fan selection won't ever come off the high (noisy) speed.

Is the fan supposed to slowly go down as the heat in the cabin reaches the desired temp? I end up running it on LOW a lot to keep the noise level down and then don't get quite enough heat. It's -18C outside today.

Maybe there is a sensor to check/replace. Any ideas?