Coolant Fan (s) basic questions.. possible electric fan inop?

the brit

New member
I've been searching and reading, but apologies if I've missed anything.. I'm not sure if the fans on my '03 T1N are running correctly..

From start up the belt driver (viscous coupling?) fan runs, and always appears to run. I have not heard nor seen the electric fan on the exterior of the radiator run ever though.. In a recent drive through the mountains in Georgia I saw the coolant temps rise to around 220' but I still didn't perceive a change in either fan, and the electric fan was not running when I stopped at a rest stop still at this temperature.

If it sounds like the electric fan is not operating correctly (or at all), is there a thread that covers diagnosis of the related items i.e. a temperature switch, a fuse, a relay and any other related items please?


Just for full disclosure after reading another related thread (that didn't cover the system in detail), the previous owner of my van had removed the A/C compressor.. I do not know what else they removed though.
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Before you go any further, check your cooling fan's viscous clutch:

When the engine is cold and off it should spin fairly freely with a little resistance.
Then get the engine up in the 180-200 degs and shut it off, and with a gloved hand to prevent getting scorched, the fan should no longer spin as freely.
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DRB III Owner If You Need
Your electric fan is there to cool the AC condensor, meaning if the AC is not on, the electric fan will never come on.

You can wire a switch to it to make it manually come on.

You would wire it to the relay that powers the fan.


Formerly Type2Teach
I'll second what Skydiver said- the electric fan on the very front of the radiator is the AC fan and will only come on with the AC, not with the engine temp. :thumbup:
I'll second what Skydiver said- the electric fan on the very front of the radiator is the AC fan and will only come on with the AC, not with the engine temp. :thumbup:

FYI this was the thing keeping my engine from overheating further with a bad viscous clutch... running the A/C which runs the fan.

In my water-cooled VW I turn on the A/C (which is no longer connected) to run the fan when doing long slow off road hill climbs.

Aqua Puttana

Poly - Thread Finder
While adding some info to one of my reminder notes docs I stumbled across this tidbit. Maybe it will help others...

Some checks and info for A/C Controls and Aux. Cooling Fan

Text from the post:

"Just my 2 Cents: 1. my 2006 was overheating 240 F 2. When AC was on I noticed AC condensor fan was not coming on .. along story short ..yes the wires do vibrate causing some exposure.. a quick way to test if the if fan is operational without hot wiring is unplug the sensor on thermostat housing this will engage the ac condesor fan. .... After hours of checking all fuses and bypassing relay #4 fuse (tip: the [85/86/87 style control] relay can be matched up with generic from local auto parts store does not need to be mercedes brand) ... and alot of bad words ... I finally came to the conclusion that it just could be a bad ECM [ATC]approx replace cost $400 ( electronic control module ) Which is the electronic board behind your temperature control guages .on dashboard.. so I took it out of the dashboard unplugged it .. as I was looking at the contacts I noticed alot of wear on contacts so I unplugged it 2-3 times and plugged it back in .... well would you know it worked .... so what Im guessing is that from all the vibrations this damm thing was making proper contact so it wasnt closing the circiuts in the relay so it wasnt turning on ac condensor fan ."

Andy, Thanks for the temperature operation reminders. :thumbup: vic
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New member
Thanks to all responses above. You learn something everyday. I'll run my Sprinter up Ute pass, with AC off and then AC on and listen for the AC Aux fan to come on...can't mistake it, they are pretty loud, sounding much like a jet engine winding up. :bash:

Aqua Puttana

Poly - Thread Finder
My cooling fan wasn't working so yesterday I tore into it. Unplugged the dryer plug, nothing. Unplugged the plug on the t-stat. Nothing.

Ended up pulling the grill and had power going to the plug so the fan is toast. Now I need to figure out how to get it out. Time to search.


Erratic Member


Erratic Member
Thanks. I don't have any luck finding the procedure in the service manual. I'll figure it out.
They do hide it well.... it's on page 24- 70 (in the air conditioner plumbing section)

... that's page 1404 by Acrobat's page-counter.

(in the "how to remove the A/C condenser" section)


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