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What else can be wrong with AC/AUX fan...

7K views 32 replies 8 participants last post by  coolchu 
#1 · (Edited)
I've been trying to tackle the issue with AC in my 2003 540i.

I've looked at numerous threads and videos about diagnosing my issue.

Here's what's happening:

  1. The AC function appears to activate: I notice there's a bit more airflow when AC button is activated.
  2. AUX fan does not turn on regardless of car's temp or AC is on or off.
  3. AC clutch does not activate when AC button is pressed.
  4. External temp sensor was replaced and shows proper outside temp.
  5. AUX fan is not seized, can be rotated easily

Here's what I've done so far:
  1. Tested AC clutch with direct 12V - clutch activates (can hear it click).
  2. Tested the lead to AC clutch but is only at 5V regardless of AC being on or off
  3. Tested (was good) and swapped out lower radiator temp sensor (AKA AUX fan switch) - AUX fan still does not turn on.
  4. Checked leads and plug to AUX fan, it gets constant 12V at plug but does not seem to activate fan; third wire has 5V going to it (I assume this wire sends the signal to the fan's "CPU" to turn it on).
  5. Checked AC charge and recharged it to 40psi.
  6. Checked blower fuses 75 and 76. Checked all AC related fuses in glove box (9, 20, 7, 20, 22, 23)

What other issues can be wrong with the AC system? Does a clogged/stuck compressor prevent the car from turning the AUX fan on?
 
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#2 ·
Third wire is to dme. There are tons of trouble shooting threads on the dme controlled aux fan. If I remember correctly, with the car at op temp, engine off, key in pos 1 and hvac panel off, when you unplug the lower coolant temp sensor the fan should spin up. If not, ded. You most likely need a new fan
 
#4 ·
The dme controlled fan doesn't care about the air conditioning, from what I understand. When the temp sensor sees a certain coolant temp, it calls for the fan to spin up regardless of air con settings. The a/c does depend on the aux fan passing the self- test upon start up, if I'm not mistaken. No aux fan function, no air conditioning. Did you vac your refrigerant down and refill with the correct amount? Or just top it off?
 
#5 ·
The dme controlled fan doesn't care about the air conditioning, from what I understand. When the temp sensor sees a certain coolant temp, it calls for the fan to spin up regardless of air con settings. The a/c does depend on the aux fan passing the self- test upon start up, if I'm not mistaken. No aux fan function, no air conditioning. Did you vac your refrigerant down and refill with the correct amount? Or just top it off?
benny...which one..? the rad hose or w/p mounted one...?
 
#7 ·
#11 ·
If you didn't evacuate the system then you have 40psi of something. Most likely air and moisture. Start by having a shop vac the system and refill to correct amount of r134a. This will also have the bonus of removing moisture from the system and adding dye to further trouble shoot.
 
#15 ·
It's possible that the HVAC panel won't energize your A/C compressor clutch because the aux fan is inop. It happened on my '03 530 (although others have reported that their car with PWM controlled fans will run the compressor with an inop aux fan - version or software revision?) When the HVAC wants to engage the A/C compressor it signals the DME, the DME increases idle RPM slightly and signals back to the HVAC panel "OK to engage A/C", the HVAC panel puts B+ to the compressor clutch. But if the DME has determined the aux fan is inop, it doesn't "authorized" the HVAC panel. In my case I confirmed the aux fan failure with INPA and a new fan solved the A/C problem.

Your PWM controlled fan is run by a signal from the DME which is determined rad outlet temp (as edjack mentioned) as well as A/C system pressure. The DME starts the aux fan on slowest speed only after A/C pressure reaches 5 bar (~75 psi) and then ramps up as pressure increases. OTOH, the earlier relay and resistor controlled aux fan activates the aux fan the instant the A/C clutch is activated even if A/C is inop. And A/C is activated even if the aux fan is inop.

A full featured BMW compatible diagnostic system will:
- report a fault if the PWM aux fan is inop. (a generic scanner won't necessarily report this fault)
- have a test procedure to activate the fan as a positive test, i.e. see it run even though temp and/or pressure are below thresholds
 
#16 ·
WHen my 528i ac clutch wasn't working, I pursued all the AUX fan, pressure sensor, relay etc options. Turns out that it as the HVAC controller as all that remained - ie 'when you eliminate all the probably and possible, whatever remains (however improbable in your mind) is the answer. I bought a used controller, installed it, and the AC came on right away.
 
#18 ·
I was able to charge my AC to the correct pressure.
I was only able to do this while having a 12V directly hooked up to the compressor clutch. The wire going to the clutch was only 5V.
I was also able to see the AUX fan run for the very first time!
The air was also very cold!
However, once it was charged, 12v wire removed, and hooked to the original clutch wire, the compressor never seem to kick on.
The wire going to the compressor clutch never goes over 5V so the clutch does not activate despite having charge. All fuses seem to be OK as well.
I do hear the car being a bit louder and more air flow when AC button is pressed.
 
#20 · (Edited)
When you press the AC button, do you have power to the compressorr? Put a digital voltmeter on the wire and see. My problem was that the HVAC controller wasn't working properly. And, new parts don't always work anymore. Don't just assume - check. The fact that you measured 5V suggests that it isn't. (was that the "new" or old HVAC controller with that reading.

Maybe it's time for a summary post listing numbered point by numbered point what you have done. I can't tell - but have you jumped the AUX fan switch (not the resistors) to see if the fan runs when it has power?
 
#27 ·
I see. I had the same symptom - a low voltage on the compressor wire. I changed the HVAC controller because everything else checked out.

As S. Holmes says (to paraphrase): "When you have eliminated all the possible and probable, whatever is left (no mater how unlikely seeming), is the solution.

Do as others suggest for your peace of mind. Get the system properly evacuated. Recharge it to the correct weight (not pressure) of refrigerant as listed somewhere in your engine bay with a green tag (IIRC), and see if it runs.

I didn't bother testing the pressure switch because they are unlikely to fail, and they are very very difficult to detach to jump the pins. Plus, they are variable in terms of throughput, and there is some question about whether or not they can be damaged by jumping (Im agnostic on this).
May have to try a third HVAC controller after vacuuming and refilling the system. Can the HVAC with the "REST" function interchange with the "MAX AC" one? My car currently has the "MAX AC" unit. The "REST" units are easier to find and cheaper in most cases.
 
#19 ·
Ok.. sounds like you have complicated 1 problem in to a few others..

you need to work with a known good Ac system, evac, and charged correctly
you can take a wire and jump out the Ac pressure switch, (this will eliminate your incorrect charge procedure )

you then need to get the car to temp, once @ temp and with the AC jumped out, the DME will think that the system is @ pressure and ready to operate, THE Ac compressor should turn on, and then you should have met all the requirements, for the fan to spin

you then need to confirm that the fan is getting the correct 10-100mv single from the DME, which can be viewed on any volt meter that will Read DC' Hz

The connector for the FAn should have a Live 12vDc wire, and a Good Earth, the blue wire (smaller one) is your signal, you will go across that and earth


Im going to lean with a system that has not actually been evacuated and recharged correctly



Rent a vacuum pump, suck that thing out for about 2 hours, Then buy 3 cans of r134a put in 2 can's and wait on the 3rd

(you can honestly evac and recharged these systems with out guages, they are pretty fricken panzer)
 
#24 ·
Ok.. sounds like you have complicated 1 problem in to a few others..

you need to work with a known good Ac system, evac, and charged correctly
you can take a wire and jump out the Ac pressure switch, (this will eliminate your incorrect charge procedure )

you then need to get the car to temp, once @ temp and with the AC jumped out, the DME will think that the system is @ pressure and ready to operate, THE Ac compressor should turn on, and then you should have met all the requirements, for the fan to spin

you then need to confirm that the fan is getting the correct 10-100mv single from the DME, which can be viewed on any volt meter that will Read DC' Hz

The connector for the FAn should have a Live 12vDc wire, and a Good Earth, the blue wire (smaller one) is your signal, you will go across that and earth

Im going to lean with a system that has not actually been evacuated and recharged correctly

Rent a vacuum pump, suck that thing out for about 2 hours, Then buy 3 cans of r134a put in 2 can's and wait on the 3rd

(you can honestly evac and recharged these systems with out guages, they are pretty fricken panzer)
How do you jump out the pressure switch?
Can the pressure switch be replaced without evacuating the system? Is there a way to test it without removing it?

part 10??:
http://www.realoem.com/bmw/enUS/showparts?id=DN53-USA-02-2003-E39-BMW-540i&diagId=64_0788
 
#28 · (Edited)
I don't know. Your system is a lot more complicated than mine with the entire DME intervention thing. Mine is much more mechanical. If you're going to vacuum the system. maybe you should take the chance to test the pressure switch, just in case.

Here is a summary of the crap I wrote below:
1. You can find out which HVAC controllers can substitute for yours on REALOEM.com, described below.
2. My HVAC controller issue resulted in a Fault code 6 in INPA in the HVAC module (can't remember what it was called).
3. You can check if your AUX fan works from the DME by watching it when the car is cold-started It spins briefly at 20%

I hope this helps somewhat.

As to the HVAC controller. If you go into Realoem.com with your last 7 characters of the VIN, and look up the HVAC controller - you can get the part number. If you type it in the part number box, you can see a list of all of the "supersedes and "retrospective", along with an indication of whether or not it is backward compatible or not. This will then give you a choice of part numbers / HVAC controller types that you can use.

BTW, you had cold air when you jumped the AC - so what vacuuming and recharging the system will do for you is to make sure that you have the proper amount of refrigerant BY WEIGHT.

Also, IIRC, the DME checks the fan (at startup maybe - or when the key is turned to one of the positions? ) I would suggest finding out when that happens and get someone to do the action while you watch the fan. This will tell you if the DME has control or if the issue is with the DME connection.\

I don't know what research you've done, but the following links are to threads that may be related to your issue. Sorry, if this is redundant.

This thread is all my trials and tribulations with the AUX fan, overheating, AC not working. This post in the thread talks about an INPA fault code 6 that was resolved by replacing the HVAC controller - which I eventually did.

This link describes the DME algorithm for operating the AUX fan - which includes AC pressure. It also mentions that the fan is operated briefly at 20% when the car is started. So, you can check the AUX fan that way from the DME perspective.

Blown fuse 75 for Aux fan found by testing for power at wires - even with car off.

This link is to a post about why needing between 10% and 90% signal to test the DME controlled AUX fan.

This link says that you can test the AUX fan from INPA.
 
#29 ·
I believe you reported the aux fan works when you put 12v on the AC clutch. This seems to rule out an aux fan problem.
So you've tried 2 IHKA modules w/o success?
What ambient temp does the OBC show? If system thinks amb temp is below ~40F, due to a missing or damaged temp sensor, the AC clutch won't engage.
 
#31 ·
Brought the car to an indy shop, they found there was water entering through the firewall. The water damaged some wiring to communications modules near the driver foot well. Fixed the firewall plug and rewired the connections. The A/C is now working!
 
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