W126 SEC auxiliary fan replacement

Once I got the air conditioning working on the 560SEC it was apparent the auxiliary fan was not working.   As can be seen in the wiring diagram below, the W126 SEC auxiliary fan can be triggered either by high coolant temperature or by refrigerant pressure.   The diagram is for 1986-1990.   In 1990, the W126 went to a dual fan setup.    The fan can operate at two speeds based on a resistor.

My fan would not work even when fed 12v directly.   I struggled to find a replacement fan from a brand I trust.   I wasn’t that keen on a used fan as they are all now quite old and in the hot Australian climate run quite a lot.   In the end all I could find for a reasonable price was Meyle fan.   Meyle is a brand I normally try to avoid as I have found the parts are not a great fit.

The W126 SEC auxiliary fan is not as easy to remove as on a four door car as there is less room to maneuver the fan.   The fan itself is held on by three 8mm bolts.   Two of them can be seen in the picture below.    They are at 2, 6 and 10 o’clock on the fan.   The fan is not bolted on directly, in all three cases there is a mounting bracket.   For the 6 o’clock mount, it is easier to remove the mounting bracket with the fan.   This is a 10mm bolt that is obscured by the bumper.

Once the fan is loose, it is a bit of a chore to actually remove it.   I found the easiest way was to move the strut out of the way that mounts the horns and loosen the panels that go under the headlights.   The strut has two bolts holding it on and there are three to remove to loosen the panel.   It was quite dirty underneath the old fan so I gave it a quick clean out with compressed air.

Once I had removed the old fan I was able to compare it to the new Meyle fan.   The central ‘hub’ unit on the Meyle fan is a little smaller which makes removal a bit easier.   The Meyle fan also has a balancing attachment which the factory fan did not need.  Both fans do not space the blades evenly around the hub.   The factory fan also had some little felt pads to protect the condenser.

The original fan has a finger guard, which is removable and I had planned to re use it.  As usual the I had fitment issues with Meyle parts – I could only ever get two of the mounting points for the guard to line up at any given time.   When not mounted properly there is too much risk of the fan fouling on the guard so in the end I had to fit the fan without.

Installation is generally the reverse of removal.   I found it easier to start with the 2 o’clock mount loosely, then the 6 o’clock mount.   I loosely re-installed the horn strut before loosely fitting that mount before finally tightening it all up and replacing the bolts on the under light panel.    it is quite easy to push the electrical cable through to where it plugs near the receiver drier.

It’s a shame I could not fit the finger guard.   It would be hardly noticeable I have an aftermarket fan if that was the case.    The next step was to test the fan.  I went for a 20 minute drive in very heavy traffic with the A/C on full.   I brought the car back and left it to idle for a few minutes.   Sure enough, the fan kicked on and slowly lowered the temperature.   Before I replaced the fan it got so hot I would have needed to either drive or shut off the car.

I was expecting to need to do more electrical troubleshooting once the new fan was fitted.  I was pleasantly surprised to see it whir into life after the car got nice and hot.   My next step will be replace some of the climate control vacuum elements which are preventing my centre vent from working.     I’ve kept the original one to see if it can be repaired.   The auxiliary fan in my 300SE occasionally pops the fuse so it will probably need replacement at some point