aircon - fan when should it fire up?
 

Hello to all, cut a long story short (long story included below to be honest) how long after you turn on the air con in the cabin should the large fan in front of radiator fire up? Air con guy says I may need new one due to below observations….

summer kicked in early here 33C too hot, and my aircon refrigerant was low again takes two years to need a top up or refill, still not sorted it, on my visit this time to another guy who deals with aircon and car electric repairs, the minute he finished and fired up engine and turned aircon on to about 20c he said I had an issue and pointed to the large fan in front of radiator not spinning….before he could go any further it kicked in and started.

He told me to keep an eye on aircon in cabin and if I did not feel it cooling to turn off the aircon, as the fan maybe faulty and so not cooling the condenser so not cooling the car.

I did a couple of more tries whilst driving on the way home and it seemed to be working fine.

Got home turned off engine then tried after 30mins whilst checking fan in front of radiator, this time it took anywhere between 15-45 seconds to kick in, on most occasions it tried to spin and seemed hesitant as such….I also noticed that upping the fan speed on the air con output controls in the cabin made it ‘kick in’ faster.

No idea how quickly the fan for air con purposes should fire up or what else maybe wrong?ANY input great

If the fan is faulty it can be read with software that is specific to BMW. It will not trigger an OBD II code since it is not emission related. The fact that your fan does come on means the fan is working. You can command to run the fan if you have the right software.

But to answer your question when the engine is started the DME sends a command to the fan to turn it on ( it may make 1 or 2 revolution). The fan sends a signal back to the DME that it has turned on there are no fault.

The fan only comes on when there is insufficient air flow to cool the condenser. If you are driving at speed, the fan is not needed to cool the condenser and may not come on (depending on the outside air temp).

The speed of the fan is controlled by the DME. It uses a pulse signal to vary the speed of the fan. That is why there are three wires to the fan, a plus wire, a negative wire and the signal wire. The longer the pulse the faster the fan will run.

Uapllnight-superb explanation much appreciated, just to get this straight, the fact that the fan jerks slowly to try and start 1 or 2 or 3 times as i called it acts hesitant, and does not fire up as soon as the aircon is switched on is not that much of an issue? I am going to try on wifes bmw e46 and see if hers fires up straight away....again thank...

Ditto upallnight..the variable speed aux fan used after 9/1998-up (like in the M54/M52TU/M62TU/M57/M57N/N62) is controlled by the ECU/ECM/DME which sends a PWM signal to the aux fan to turn on under specific circumstances (approx 4-5 criteria).

The aux fan is not like the 2 & 3 stage aux fans used in earlier BMW models with the M62/M52/M50/M30 engines.

And at start up...the aux fan will turn on briefly as a test for the DME to know that the aux fan is okay:

Just stealing OP's thread for a minute, to state that i don't have an aux fan at all on my Europe spec. 2004 4.4 (N62).
Still, my aircon has always been working flawlessly. Even in 30 C. (86 F.) it provides plenty of cold air.

Yes...it is freaky that the n62 doesn't have the aux fan...especially when you come from previous BMW ownership that did.

It was a great curiosity for me when I got my 06 4.4 ... I searched high & low for the aux fan...I thought that it may be hidden (sandwiched) between the radiator and the radiator fan. I eventually gave up and asked the forum if I was nuts. :D (well...I'm probably still nuts...but no, the N62 doesn't have an aux fan in front of the radiator). :)

Proof? See image of hvissoer4's engine bay...not the absence of the aux fan in front of the radiator. :)

http://www.xoutpost.com/attachments/...g-dsc00753.jpg

Holy cow, that's one clean engine bay you have there Qsilver7 , and THANKS to all for the super break down on how the aux fan works, anyhow as a test and probably not the best comparison, I tested on wifes bmw e46 318i 2002 model and low and behold the fan behaved the same on switching on the air con....wish that was the only query re her car...damn think keeps chewing and fraying the serpentine belt....another story though that

You have one of the pulley misaligned. Check the alignment.

Can anyone point me to where the main power fuse for the AUX fan is located. My fan wiring was damaged in an accident and spliced up without the 3 pin plug by the panel shop. The 12v supply to the fan is dead. If I connect the fan 12v supply directly the fan starts up and its speed is controlled by the ECU.

All four 50 amp fuses in the fuse box have continuity. Nothing is labeled AUX fan in the fuse box.

E53 is a 2006 diesel.

On USA model E53 with the 3.0 engine the BIG 50 Amps fuse for the Aux fan is located in the fuse panel in the glove box. An easy way to test to see if you have a blown fuse isa to remove the connector from the fan and with a volt meter set to volts one of the big lead will be 12 volts and the other big lead will be the ground. Insert the probes into those two terminal and you should see 12 volts.