I have a 1984 300SD and have read several discussions regarding the auxiliary fans on various models, but I haven’t seen an answer to my particular problem.

My auxiliary fan quit running. I had checked it a week ago by shorting the leads to the temperature switch on the dryer and it was working fine. I had the system recharged and now the fan does not work. I have tried grounding the engine coolant temperature sensor lead, and shorting the temperature switch leads on the drier again, but no fan.

My book does not have the exact electrical schematic for my model, but they seem to be somewhat similar. I am using the one in the Automatic Climate Control Service Manual for Model 126, labeled starting in August 1980 for the USA /J model. I have checked the voltage on both sides of fuses C, 10, and 11 and get about 10 volts so the fuses are good. (Fuse C has voltage on it even with the ignition switched off) I have checked for voltage on the connector that the fan plugs into and get zero there. So somewhere between the fuses and the fan I am losing juice. I can’t locate the auxiliary fan relay 21 to check it out. Does someone know where it is located? What about other possibilities?

Thanks in advance for you help.

Wayne