My 300SDL started to run hot at times, so I searched the forums (as always)for suggestions. I refilled the viscous clutch with silicone and then checked the electric fan. I found that the electric fan was not operating on low with the AC and would not go high when the temp rose above 105 C. Checked the fan motor and circuit breakers which checked good. I next bypassed the fan resister and swapped out fan relays, and still no go. So I reversed the wires from the temp switch to the pressure switch so that the fan runs on high when the compressor is engaged. That seems to work well. Temperature stable at about 87 C. However, I then noticed that my AC compressor is on all the time, even when I press (EC) or the off button (O) on the control unit. How is that possible? Other than running all the time, the heating/air system works well. Should I worry about it?