560 auxilliary fan

[Patrick_R]

Gents,

Can someone please let me know when my front electric fan should come on?

I drove it during the super hot 40 degree days here a couple of weeks ago with the air on, and she started to get over the normal operating temp she always sits at, this is ok, lots of bumper to bumper traffic, but I could not hear the fan?

Also, is there any tests for this unit?

Many thanks in advance.

 

[c107]

Off the top of my head there are two sensors used to determine if the fan should run:

1) coolant temperature sensor
2) A/C pressure sensor on the drier.

The fan can run at slow or full speed and there is a resistor on the left hand side of the engine bay to control this. Later cars had two fans instead of one big one that runs at two speeds.

I think from memory the coolant temp sensor causes the fan to cut in at 105c. There are two relays in the fuse box for slow/fast.

The system is often modified when the car is setup to run R134A. To get the same performance the fan is wired to run any time the compressor runs, bypassing the original system altogether. My 300SE is like this. R134A needs more airflow across the condenser.

First thing I would do is test with A/C on if you have not done so. Next the fan unpluggs near the front and you can apply 12v directly to the fan so see if it will run. You can also jump the sensor on the drier to see if it will run from there too.

It may also be worth seeing if there is an extra wire from the pos terminal of the battery like my car has. I had the same problem and the inline fuse that had been installed when the factory system was bypassed had blown.

 

[Styria]

C107, that's a great answer. I would not have been capable of anything like it. On the 6.9s, there is a switch at the front of the engine that can be changed to a unit that will activate the fan at a lower temperature. There is also a switch located on the firewall and that seems to have some function in turning on the fan when the Air Con is engaged. Other than that, I don't have a lot to say. Regards Styria

 

[c107]

For more detail, attached is the wiring diagram:

 

[Patrick_R]

Gents,

Thank you so much for your insight.

I will investigate on the weekend.