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2003 BMW 325i air condition aux fan.

Tiny
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  • 2003 BMW 325I
  • 97,000 MILES
Main problem: A/C does not blow cold air.
aux fan when car in hot weather stop/go condition. Does not operate full range of speed it should. Also when turn A/C on same pattern. Tries few rotations then stop. Over and over stop/go.
I cant reach the fan motor direct to apply 12 v power since it has a module that controls variable speed.
however can access the connector has 3 wires
one big red+ one big browm- and small black for pulse that will
control variable speed needed.
Q1. Can I apply 12v positive to red and negative to brown and test at least might be high speed mode. Then try red and small black for low speed. Not sure if pulse wire will take negative charge.
I need be absolute sure aux fan is malfunction.
(already checked external temp sensor ok, compressor clutch rotating, freon has correct pressure, a/c fuses ok.)
Q2 Any way jump A/C relays to bypass aux fan and see if can get cold air out of A/C? I understand A/C designed not to function if aux fan is defective.
Thanx
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Wednesday, September 11th, 2013 AT 1:14 PM

10 Replies

Tiny
TY ANDERSON
  • MECHANIC
  • 719 POSTS
Does your 325i have a manual air condition system or does it have a automatic feature. There are two types of wiring diagrams specific to each system so I need to know which one to provide accurate information to you. Let me know, TY
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Wednesday, September 11th, 2013 AT 6:36 PM
Tiny
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Thats surprise question. Its my daughter car and I would say its manual. Since the few times played with A/C controls never seen any indication of automatic setup options. Just in case will check manual. If automatic will let you know asap.
Tx
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Thursday, September 12th, 2013 AT 12:57 PM
Tiny
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MANUAL HAS SECTION AUTOMATIC CLIMATE CONTROL.

SEPARATE SECTION FOR AIR CONDITIONING.

THEREFORE WOULD BE MANUAL AIR CONDITION.

TX
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Thursday, September 12th, 2013 AT 2:54 PM
Tiny
TY ANDERSON
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Ok thank you for that.
Power and ground is already applied to the aux fan all the time. The vehicle's computer controls the fan speed via signal wire (black wire). The few ways to test this fan is to command it on with a scan tool or take the fan apart to get access to the fan motor electrical terminals to bypass the electronics in the fan or what is called "fan module". Applying power to the fan motor electrical terminals will only tells you the fan motor works or it doesn't, It doesn't tell you if the electronics in the fan module are working properly or the digital motor electronic control unit. Unfortunately, I don't see a way to jump a relay to get the cooling fan(s) to come on other that what I've just mentioned. Hope this helps, TY

The vehicle's computer controls the digital motor electronic control unit (dmecu) and dmecu controls the fan control module (if that makes sense) via pulse width modulated signal. This is how this cooling system is broken down into several control modules to perform specific operations under certain conditions.
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Thursday, September 12th, 2013 AT 10:14 PM
Tiny
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Got it. However what I meant about jumping relays was not to get aux fan turn on. Wanted to see if can jump relays (bypass in some way the aux fan) to force air conditioning to activate and blow cold air few minutes as test to confirm its the aux fan is culprit and not other issue.I.E. Pressure sensor, temp sensor, compressor itself bad (even though clutch is rotating) etc from what I understand BMW designed A/C not to operate if aux fan is defective. So if I can temporary bypass aux fan, A/C should be able work ?. Of course sounds to good to be true.
TX
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Friday, September 13th, 2013 AT 3:36 PM
Tiny
TY ANDERSON
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If the a/c compressor clutch is engaged and spinning it should be cycling refrigerant, as well as, the pressure sensor in the a/c pipe is saying it's ok for the compressor clutch to engage and spin. So, if your are traveling at freeway speeds and the compressor is on you should be feeling cold air. With the engine running and a/c on (make sure the clutch is spinning) feel the a/c hoses. There is a larger diameter pipes and smaller diameter pipes? Do you feel any pipes that are cold at all? If so which one. Take care around a running engine for anything that could harm you. Talk to you soon, TY
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Saturday, September 14th, 2013 AT 12:09 AM
Tiny
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I did check when turn on A/C, clutch does spin. However supposedly since aux fan is confirmed defective (stop/go pattern will not stay on spinning when A/c engaged). Then there is no way check cold air. Since from what I understand BWM designed it so if bad aux fan, then a/C shuts down. Thats why was wanting find out if can bypass aux fan. Jumping fan relays? Or whatever other possibility
to see if can get cold air out of A/C.
Then can at least know its not pressure sensor or coolant temp sensor, etc
Tx
Albert
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Wednesday, September 18th, 2013 AT 2:17 PM
Tiny
TY ANDERSON
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The aux fan is controlled completely by the vehicle's computer. There is no relay terminals to jump to get the fan to come on. The only way I know to command the fan on is with a compatible scan tool. I'm guessing you might be able to take apart the cooling fan module to gain access to the fan's power/ ground terminals and power up the fan by making your own temporary circuit connected to the vehicle's battery. Unfortunately, the way BMW has engineered their electronic control systems is control module communicating data to control module through CAN networks. Most vehicles have a fail safe mode specifically with the front defogger. Can you get that to work and does it blow cold?
Another option maybe to have the Climate control system scanned for fault codes (with a compatible scan tool). This particular system will store fault codes when they're detected. A particular code will direct you where to start diagnostics with diagnostic steps to take, so if you can get a code(s) I can help you through the diagnostic steps.
Start here and get back to me, TY
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+1
Wednesday, September 18th, 2013 AT 6:39 PM
Tiny
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So you are saying to test operate front window defogger using its own switches to turn on.I am not activating the A/C unit.
Hope I got it correct. On this basis will test and report back.
Will either blow ambient temp air or cold a/c temp air.
Sounds strange defogger would blow cold (A/C temperature) air
on its own. But thats why you are calling it a fail safe mode.
Tx
albert
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Thursday, September 26th, 2013 AT 7:44 PM
Tiny
TY ANDERSON
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Yes, turn on the a/c system and switch to defog. The a/c system removes moisture from inside the vehicle thus blowing dry air at the front windshield removing fog from the inside of windshield. These are the only options that I know off to isolate the cause from what you've been able to communicate to me.
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Friday, September 27th, 2013 AT 6:04 PM

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