jrr4948

I have a 1991 W124 300E 3.0L Base. I replaced both auxiliary fans with new units. Tested both before installing. I also have a jumper switch to keep them on regardless of temperature. The passenger side works however the driver side is off. What do I check before I have to rip this all out. Are there separate relays? I read they are in parallel therefore all on or all off correct? I checked the inline fuse - good. The connector before the fans turns off the passenger side when disconnected and back on when connected but the driver side is still off. If I pull the first relay the passenger side shuts off as well and back on when reconnected. Any suggestions would be appreciated! Thank you. JRR

Plutoe

Take the jumper switch out and return the circuit to the original design--then go to wikipedia and read the definition of "auxiliary fan"---you will note that the fan is designed to come on\off when two different cooling systems exceed their design limits---they are not designed to run ALL THE TIME!!

jrr4948

I can appreciate your comments regarding design however this limits were designed for high speed highway driving. In my case in NY I am cruising in 90 degree heat at 15mph in bumper to bumper traffic On a good day!!!. The Fan clutch is not sufficient to properly cool the radiator. The pressure is rising and my sight glass started to leak and the drier had to be replaced along with a flush and refill for $120! I have a dash switch to turn on the aux fans for these purposes to cool the radiator when stuck in traffic which can be often. Again my question is when the fan is on are they independent or should they both run together if on? I am going to have to check the plug under the driver fan for continuity if this is the case since it is new and was tested before I installed them both. Thank you...JR

optimusprime m1

Hot wire them both to a switch on your dash board ,so you can put them on when needed.

Hanno

They run together, both at a high or low speed, but always together. There is one main feed harness: it services both fans. It starts at the 2 pole connector near the AC pressure switches. The main feed then splits into two 2-pole connectors, one for each fan. As you tested both fans before install, you may not have plugged one in, it's connection surfaces may be corroded, or the harness has a fault. Unfortunately it's a royal pain to access the fan plugs when already installed.