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Discussion Starter · #1 ·
First post so please be gentle....
The patient is a 2001 325iXT with about 105,000 miles. New to me with a good service history. Recently the weather has warmed up and I tried the AC for the first time. Blower motor runs but air temp at the outlet is not cold. (Maybe a slight bit cooler than ambient.) I've been reading many posts about the AUX Fan but find them contradictory.

Here are my symptoms (Outside temp about 80 degrees):
  • No fault codes showing.
  • Controls set to AUTO and desired Temp set to 59 degrees - coldest it will go.
  • AC ("snowflake") button is on and button LED is on.
  • Compressor clutch does engage and spins the compressor when the AC button is on.
  • AUX Fan does NOT turn on when compressor is spinning. (Should it be on when the AC is on? Some say yes and others say no.)
  • Unplugging the lower coolant hose switch as no effect.
  • After about 3 minutes approximately, one line going into the condenser is hot and the other is about ambient temp.
  • After warming for a few minutes, the Aux Fan begins to cycle. It runs for about 10 seconds (looks like at slow speed but smooth, quiet and steady) then it turns off for about 10 seconds then on for 10 seconds, etc.
  • When the fan cycles, I can hear a relay clicking on & off. (Sounds like it is near the firewall?) Assume this is the fan power relay and it is controlling the fan as it should. (However I've read the fan has power going to it all the time so what is the relay doing?)
  • Have not checked the Freon pressures yet. Waiting for hose adapters for my vintage R12 manifold gauge set. However there must be SOME Freon because the compressor is staying on and the hose is getting hot.

My assumptions:
  • The fan motor is OK because the fan spins sometimes.
  • The fan fuses (under glove box?) are OK because the fan spins sometimes.
  • The fan wiring is OK because the fan spins sometimes
  • Fan control relay is OK. (Clicks when the fan turns on and off.) (Does this relay send power to the fan?)
  • The fan is spinning occasionally because the hose temperature switch is cycling it on and off - right? (The 10 second fan cycles are very short for there to be much cooling so maybe this assumption is wrong.)
  • IF the cycling is due to temperature, then communication to the control computer (DME? ECU?) must be OK. Right?

Not sure where to look next. (I'll check the gas pressure when I get the adapters.)
Any help would be greatly appreciated.
Dennis
 

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BeeemerBro
5,4,6 BMW X3 All...196K +
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Ok I'm researching this as well...

I've found that fan can be bad #1even if it spins (constantly that is)
#2even it doesn't spin...at all!

The fan spinning should fluctuate.

There are over seven different speeds the fan can respond to depending on the command from the dme (car's computer).
Also...there is no relay for the fan but a speed control unit.

I suspect for you this unit maybe on its way out...tell me does the fan come on shortly after the ignition is on.
For me when I turn the ignition on, and on my way out the car the fan is beginning to start. It stays on for maybe 60sec, then slows to a stop.
This self check is normal.
 

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Discussion Starter · #3 ·
  • Don't understand how the fan motor could be bad if it spinning smoothly?
  • Tried the self check once and didn't see the fan spin. Maybe I missed it.
  • Did a quick check of low side line pressure with the simple gauge that comes with a can of R134a. With the car off, there was very high pressure on the low side. (Maxed out the gauge.) With the engine on and the compressor running, low side dropped to about 30 psi -- the low end of the green section on the gauge. Don't have the hose adapters yet to check the high side.
 

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Wingnut
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the refrigerant pressure equalizes thru the system when its off, therefore the high pressure youre first showing, the gauge probably maxes out at 60 psi or so. static pressure once equalized is usually around 120-150 psi.once running, it differentiates between the hi and lo sides. what youre seeing is normal in that, possibly somewhat low on charge. the pressures arent absolute, one needs to monitor the vent temp and figure in the ambient temp for calculating pressures, what youre seeing if pretty normal. the proper way to recharge a system is to evacuate it all out, put the system under vacuum for a period of time to remove and moisture, and recharge with the proper volume by weight of refrigerant.
the aux fan does a self test when the car is initially started, controlled by the DME. its energized for a short time period, then monitored during spin down for back emf feedback by the DME to see if it reached speed. the fan is controlled by a PWM signal supplied by the DME, the duty cycle of the PWM signal is what controls the speed variance. if it fails self test, a code is set in the DME for the aux fan, ne CEL is set. your fan should have a 3 pin connector, +12v, common and the PWM signal(the small wire)
 

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BeeemerBro
5,4,6 BMW X3 All...196K +
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  • Don't understand how the fan motor could be bad if it spinning smoothly?
The properly functioning bmw fan is one that not only spins but one that spins @ various intervals.
From what I've learned is that the unit that reads and interprets the speed signals from the cars computer can not be repaired or replaced therefore a new fan is required. Sure the fan functions but not as it was designed to.
 

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Discussion Starter · #6 ·
Thanks for the replies...
The electric AUX fan does not seem to "self test" on startup. (I start the car and no fan rotation.) I don't have access to an OBD reader right now, but no fault indication is displayed on the dash.

mattmar1 do you mean there could be a stored fault, but no Check Engine Light message will display? Will a basic OBD reader pick this fault up?

I know the aux fan spins if I let the engine run for a few minutes, so I assume this rules out a bad fan motor, fuses and power wiring. But BimmurBrothor you're saying the fan has built in controls that could still be bad even though the motor is spinning? Yes, there might be a problem with the control signal from the DME to the fan keeping it from running, but the fan motor itself has some additional integral controller that can't be replaced independently?

Without BMW's computer and/or software is there a way to monitor if the control signal is getting to the fan?

Assuming there is no signal to the fan - either during self testing or with AC on - does this mean either a wire/connector problem from the DME or a bad DME? Is there something in between the DME and the fan plug?
 

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Discussion Starter · #8 ·
I do have a Fluke 189 that can measure a frequency signal, though I've never used it for that. (I'd have to do some homework.) What signal should I be looking for? 5V? 12V? Frequency range?

Assuming I can figure out how to use the meter, where do I look for the signal and when should it be present?

("Go Wings!" A fellow Detroiter?)
 

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I do have a Fluke 189 that can measure a frequency signal, though I've never used it for that. (I'd have to do some homework.) What signal should I be looking for? 5V? 12V? Frequency range?

Assuming I can figure out how to use the meter, where do I look for the signal and when should it be present?
Dig through the attached PDF and find the section on your specific fan. The thick wires will (almost certainly) be 12V and ground, while the thin wire will be the PWM signal.

("Go Wings!" A fellow Detroiter?)
You know it!
 

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BeeemerBro
5,4,6 BMW X3 All...196K +
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Thanks for the replies...
The electric AUX fan does not seem to "self test" on startup. (I start the car and no fan rotation.) I don't have access to an OBD reader right now, but no fault indication is displayed on the dash.

mattmar1 do you mean there could be a stored fault, but no Check Engine Light message will display? Will a basic OBD reader pick this fault up?

I know the aux fan spins if I let the engine run for a few minutes, so I assume this rules out a bad fan motor, fuses and power wiring. But BimmurBrothor you're saying the fan has built in controls that could still be bad even though the motor is spinning? Yes, there might be a problem with the control signal from the DME to the fan keeping it from running, but the fan motor itself has some additional integral controller that can't be replaced independently?

Without BMW's computer and/or software is there a way to monitor if the control signal is getting to the fan?

Assuming there is no signal to the fan - either during self testing or with AC on - does this mean either a wire/connector problem from the DME or a bad DME? Is there something in between the DME and the fan plug?
If the fan spins constantly or not at all...the there's a problem.

Read this one encouraging...

 

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BeeemerBro
5,4,6 BMW X3 All...196K +
Joined
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4,971 Posts
Thanks for the replies...
The electric AUX fan does not seem to "self test" on startup. (I start the car and no fan rotation.) I don't have access to an OBD reader right now, but no fault indication is displayed on the dash.

mattmar1 do you mean there could be a stored fault, but no Check Engine Light message will display? Will a basic OBD reader pick this fault up?

I know the aux fan spins if I let the engine run for a few minutes, so I assume this rules out a bad fan motor, fuses and power wiring. But BimmurBrothor you're saying the fan has built in controls that could still be bad even though the motor is spinning? Yes, there might be a problem with the control signal from the DME to the fan keeping it from running, but the fan motor itself has some additional integral controller that can't be replaced independently?

Without BMW's computer and/or software is there a way to monitor if the control signal is getting to the fan?

Assuming there is no signal to the fan - either during self testing or with AC on - does this mean either a wire/connector problem from the DME or a bad DME? Is there something in between the DME and the fan plug?
Read this one totally...
 

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Wingnut
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Thanks for the replies...
The electric AUX fan does not seem to "self test" on startup. (I start the car and no fan rotation.) I don't have access to an OBD reader right now, but no fault indication is displayed on the dash.
mattmar1 do you mean there could be a stored fault, but no Check Engine Light message will display? Will a basic OBD reader pick this fault up?
Without BMW's computer and/or software is there a way to monitor if the control signal is getting to the fan?
yes if the DME detects an aux fan issue, a code will be set, but no CEL lit up, as its not an OBDII fault. a basic code reader will read the aux fan code, as well as others that dont fall under the protocol for a CEL.
the PWM signal is 5v, 10 - 100 hz. the 2 thick wires are the 12v and common, the thin wire the PWM from the DME.
 

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Discussion Starter · #14 ·
Thanks for the signal parameters. Now I have to learn how the use my meter to read them!

The attachment TheHockeytowner sent is great. I have a much better understanding on how the system was designed to work. Wish I had the ability to talk to the DME for troubleshooting, but I think I understand enough now that I can attempt some tests.
 

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Wingnut
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that fluke is a nice meter, itll get you what you need here.
you might give thought to getting INPS or PASOFT (BMW scanner 1.4), theyre available for free online, just the cost to you of the cables, each requires a different one. youll need a laptop to install them on to. if youre gonna diy, those will give you the ability to read the codes, in more detail, in all modules of the car, not just the engine. oh ill bet youll get a DCS or the ABS trifecta at some point, and the BMW specific capability of those two is necessary. foxwell and autel make decent ones, i cannot recommend the creator brand, it gives erroneous readings and even though it advertises that it can be updated, ive not as of yet met anyone that can update theirs.
 

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I had a 2005 e46 purchased new and sold last year. Anyway I had a similar issue for the last 3,years. All the above in is excellent. I would try recharging first before delving into the fan. Also, if you don’t already do it leave the ac/ climate control on all year round, just change the temperature it’s better for the system.
 

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Discussion Starter · #18 ·
A little more data:
1. Unplugged CTS, started car, let idle for about 15 seconds then turned on AC. Fan did start, but seemed to run at a slow speed.
2. Pulled the three wire plug to the fan at the radiator. Very clean inside. Had 12.6 VDC across brown and red/blue wires. Checked the black wire with the DMM. Was definitely getting a pulses signal. (Don't know how to use the meter completely, so couldn't tell frequency or duty cycle yet.) Looks like the pulse is getting from the DME to the fan controller. Is this fan mounted controller called the "final output stage"?
3. My fan appears to be a Bosch Gen 2
 

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Discussion Starter · #19 ·
Success...
The fan is working!

Finally got my gauge adapters and checked the refrigerant pressures - both sides were low. At an ambient of about 75*F, the low side was at 26 psi and the high side at 115 psi. Should be more like 35-40 low and 150-170 high at this temperature.

Today I bought an 18 oz can of R134a and pumped it in. (The ambient temp is about 80-82*F.) Added the full can of refrigerant and pressures went to 35 low and 224 high. AC outlet air temperature dropped from about 75*F to 55*F - MUCH better. Could hear the compressor working harder also. After a couple of minutes, low and behold, the electric fan kicked on in high speed!

I need to add more R134a charge, but I'm gong to wait overnight to see if the existing charge leaks out.

Haven't tried the fan self test at startup yet, but that may still be a problem. Don't know if it's worth chasing down as long as everything else seems to work OK and no overheating.

Side note: I did the "rolled up paper" test on the main viscous clutch fan on the engine side of the radiator. With just a couple sheet of printer paper I easily stopped the fan rotation on a hot engine. Ordered a new fan clutch.....
 

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Wingnut
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nice catch checking the fan clutch.....yeah it doesnt take much refrigerant to go from not working to working. there is only one controller mounted on the aux fan so that must be its name.
glad ya got it all figgered out. if ya get the codes checked with an OBDII reader like your local parts shop, there will be a code set if the fan isnt working at startup. but as the DME sends the same signal on the same wires for the test run as for normal operation, and as it does run, i dont see how it could be possible.
just an fyi...aftermarket fan clutches out there, especially the no name ones from the yingtongian countries, tend to not work well.
 
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