2001 540i AUXILIARY COOLING FAN DOES NOT TURN ON WITH A/C

[greh3595]

This is for a 2001 E39 540i with about 83,000 miles. A/C is all original as was the cooling system until very recently.

Last week I lost the A/C blower function, i.e., the A/C system comes on and the compressor kicks in but their is no forced air in the system. Being short of time, in a fit of stupidity I took the car to the Stealer who charged me a ridiculous amount of money to replace the IHKA Final Stage unit. Picked the car up from the Stealer and the A/C seemed to be just fine - I wasn't paying attention to whether the auxiliary fan was working or not at this point.

The next day I am driving down the Interstate and the car overheats - spewing coolant from the radiator adjacent to the inlet hose, a classic 540 failure point. Anyhow, I have replaced the radiator and other components and the coolant system is working as it should, including turning on the auxiliary fan when things get a little too toasty for the M62 engine.

However, as a result of paying attention to everything under the hood now, I realize that the auxiliary cooling fan is not coming on at all when the A/C is turned on. This is true under any and all operating conditions - hot, cold, or otherwise. I understand that the fan should, at a minimum, run in low speed mode whenever the A/C is on. The A/C otherwise blows relatively cold air, so I believe it is operating properly - I don't leave it on to long though for fear of building excessive pressure in the system and blowing it up.

Does anyone have an idea as to why the auxiliary fan is not coming on, and if so how to fix it?

Many Thanks,

[mattmartindrift]

Was the fan working before your trip to the dealer?

If yes: go back to your dealer and inform them that they didn't not properly repair the car, and discuss with them their possible role in the cause of the overheating.


I would check the motor for compression after an episode of overheating to confirm everything is as it should be.

[greh3595]

Matt,

Thanks for your comments. The fan was working correctly with the A/C before I took it in to the Stealer. I agree with your thoughts about taking it back to them; however, I am concerned that there might be something gone wrong now that they could charge me another $300 for. They are the type that are not going to admit an error or problem was caused by them. So I am hoping to be as sure as possible there isn't something else that I can just replace for far less cost than they will try to get me for.

[76papa]

My fan is new (DIY) and doesn't come on when the AC is turned on, but some BMW models have fans that respond to coolant temp rather than AC switch. Mine is a '99 528i and is supposed to have a fan switch/sensor on the lower radiator hose. I haven't investigated this yet, but will get around to it when warm weather is back next summer.

[greh3595]

Thanks 76papa,

I'm in Florida, and on my 2001 540i the auxiliary fan comes on when the A/C is turned on. I've tested the current situation on a hot 95 degree day and the fan should be running with the A/C on, but it is not. There is a coolant temperature sensor (switch) located at the radiator return outlet (lower hose). This sensor is functioning properly as the fan does turn on when coolant temperature rises above the preset level. Whatever is wrong does not seem to have anything to do with the radiator or coolant system which is working perfectly.

When the A/C is turned on, the engine RPMs increase, the compressor kicks in, the blower motor in the dash blows air over the evaporator coils and I get cool air in the car, but for some reason the auxiliary fan never comes on. This can be a big problem as the refrigerant can get too hot and basically blow the compressor, dryer or at the least a hose - another expensive repair in the making.

[chucksrt]

You could run 12 volts to the fan and see if it kicks on or check the connector for voltage when you think it should be running.

[RRDBMW]

Checked the following components if they are working - 50A Fuse, Aux Fan and Coolant Temp Sensor!

[16valex]

I would unplug this connector and have it clean real good. But definitely the aux fan should turn ON whenever the A/C is on at low speed and or idle, but not on the high way. Here's a pix of the plug.

[greh3595]

Checked the Fuses, they're good the fan is receiving power. It is a variable speed fan which I understand is controlled by the ECM. Apparently the coolant temperature sensor and the A/C compressor pressure switch all talk to the ECM which then sends frequency pulses between 10-100 hz to the fan so that it knows whether to be on and how fast to turn. The ECM turns on the Fan and regulates its speed based upon coolant temperature, air conditioning load (not sure what sort of information it is getting exactly), and vehicle speed. No way to check whether the fan is operating at high vehicle speed, at least I haven't found a volunteer willing to be strapped to the hood yet!

[RRDBMW]

Check this link -> http://forums.bimmerforums.com/forum...d.php?t=605750
There is a chance the Aux Fan Motor is the culprit....

[E39Only]

What is the outside temp? The aux fan will not kick in with a/c unless the temp is exterior temp is above 50F (not sure about the value- check bentley. Mine doesn't come on in winter.

If outside temp is low, you can use handwarmers to warm the exterior temp sensor (below the front car on passenger side).

[mattmartindrift]

I've tested the current situation on a hot 95 degree day and the fan should be running with the A/C on, but it is not.

already posted.

[Orxan4ik]

Thread revival but better than opening a new thread. If the outside temp is below 50F but the car is heating up over 110C+ would the aux still not kick in? I just discovered on my car it doesn't and therefor car overheats if I idle for a prolonged time. Fan is behr replacement I purchased 3 years ago and I have an older resistor style (05/97 prod 540iA)

Thanks in advance!

[rf900rkw]

The radiator fan isn't controlled by engine temp. It's triggered by the radiator outlet temp. So if the engine is overheating because the coolant isn't circulating through the radiator, the fan will not come on.

[Orxan4ik]

Would that mean the thermostat needs to be looked at? I get no cel or codes, car behaved fine up untill now. Thermostat is like 5-6 years old, so is wp. And thank you Randy.

It's just weird soon as I take off temp drops down which makes me think thermostat doesn't stick

[rf900rkw]

Yep. anything that will keep coolant flowing through the radiator. Low coolant, failed thermostat, failed waterpump. Or the fan switch went bad.

If you want a sanity check jump the fan switch. The should be three wires. Jumping the combinations of two should get you low speed, high speed, and nothing. The common wire for the low and high is likely brown.

Does it run hot when moving, or just sitting still?

[Orxan4ik]

Awesome info about the fan, I'll be on it over the weekend! Yes, overheats only when sitting still - soon as I move the temp drops. I think something is up a the fan itself

[16valex]

Hey Orxan. Do you still have the engine fan? I assume you don't.

[Orxan4ik]

Hey Alex, I actually do, fan clutch is good, too.

[16valex]

Hey Alex, I actually do, fan clutch is good, too.

OK, If your engine fan is good then there's no reason why you're running hot while idle, that engine fan pulls a ton of air.

I suspect your radiator maybe on its way out. Or it could also be your thermostat fails to open wide or lastly WP.

[rf900rkw]

The fan clutch responds to the temp coming off the radiator. The aux fan responds to the temp of the coolant leaving the radiator. With both in place, and it still overheating at idle, I would suspect a coolant flow problem of some sort.

[Orxan4ik]

I will start with the aux fan because that's the only thing I can see right now not turning on. Wp is Graf and was replaced along with thermostat and fan clutch in '09. The rest of the cooling including the radiator and aux fan was replaced in '11. Been working fine ever since, just overheated today while sitting in traffic. I hit the ac button but the aux fan wouldn't come on, was 45f outside. I will jump the fan to see if it works at all and go from there. Thank you guys for quick responses!

[Flounderasu]

The fan clutch responds to the temp coming off the radiator. The aux fan responds to the temp of the coolant leaving the radiator. With both in place, and it still overheating at idle, I would suspect a coolant flow problem of some sort.

Isn't the FC engaged by the temp via WP shaft?

[16valex]

Orxan, even if your aux fan died, the engine fan alone should have enough flow to cool, not unless both the aux and engine fans are dead then you have a problem.

You have a cooling flow problem like Randy said and that was why I suspected radiator, thermostat, WP or the worse case and hope not head gasket.

Check your WP for play and or sign of leakage.

- - - Updated - - -

Isn't the FC engaged by the temp via WP shaft?

No sir! rf900rkw usually right.

[Qsilver7]

Just an FYI to correct some of the info in the older portion of this thread.

The OP had a 2001 540i which would have had the M62TU engine, which used a variable speed aux fan. That fan doesn't necessarily turn on when the AC button is initiated. The variable speed fan turns on when it is sent a PWM (pulse width modulated) signal by the DME/ECU.

The 3-spd aux fan used in the 1996-1998 M62 (e38 & e39) does turn on when you initiate the AC:

The 1999 model year debuted the new variable speed aux fan: