E39 AC & Auxillary fan

[diddly]

I've searched and read enough about the auxillary fan on E39s, that I'm confused and I hate to say it; but frankly a bit intimidated by all the different info. Am I correct in deducing from what I've read, that the operation of the auxillary fan (just to be clear; I'm referring to the electric fan in front of the AC condenser) works differently on the different MY E39s? It sounds like that's the case. If someone could just answer a couple of simple (hopefully) questions for me, it'll give me a decent starting point to chase a problem or two. The car is a '97 528i. Here's what I know: 1) I just replaced the AC idler pulley and tensioner. 2) I just had the Freon evacuated and recharged by a competent pro. 3) We observed the auxillary fan running ONLY on high speed. (At least; by the sound of it; I'm betting/hoping/praying that was high speed). The engine was fully warmed up; the car parked in the garage, professional gauges hooked up to it. The high speed fan came on when the high-side pressure hit 300 psi, and continued running until the pressure dropped to ~200 psi. That cycle continued with great regularity, as long as we let it. The air was very cold inside the car; (ambient was 100 degrees). The auxillary fan NEVER ran on low speed!...Questions: 1) Should this fan run on low speed as soon as AC is called for? And if not: When? (I'm assuming it's a 2-speed fan, as I can see a resistor mounted at the top of the fan.) 2) Is the fan controlled by a couple of different relays (i.e. one for each speed), that my owners manual says nothing about? 3) When SHOULD that fan run on high speed? (Does that 300 psi 'engagement point' seem reasonable/proper? If someone can answer those questions, it'll help a lot. Ideally; hoping the problem is as simple as me: You'll say, "Yes, there are two relays; and either the low speed one, or the resistor is dead, and replacing the bad part will make everything (including me) wicked happy!" Am I dreaming? Thanks in advance for your wisdom and advice...(don't know)diddly

[RocketSurgeon]

Your car has a resistor based fan, later cars have a pulse width modulation fan. I believe that the resistors are a common failure point on that design fan, and if I recall correctly, the failure mode is high speed only. You're lucky, you should be able to fix the fan, and even if not, it is much cheaper to replace than the later design.

[rf900rkw]

It's not that complicated. '95-'98 cars have a three speed fan. '99 on have a computer controlled (PWM) fan. You have the three speed. Information on these fans is posted pretty much weekly. I posted up the wiring diagrams here.

http://forums.bimmerforums.com/forum...3#post27655843


To boil them down, again.

Normal speed any time the A/C is on, or radiator temp of 91.

Mid speed as a safety when A/C pressure exceeds 300psi

High speed is a oh crap at radiator temp of 104C



It would appear the normal speed circuit is blown. Fuse, relay, resistor. It's normally the resistor.

[diddly]

Wow...So that hurricane I heard was only second speed: It was moving plenty of air, that's for sure.
Thanks for the info. It should help a lot in finding the issue; especially since I've got the simple setup.
Are the relays located under the driver side cabin air filter housing?

[edjack]

The E-box is on the passenger side, under the air duct. The stage 1 (normal speed) and stage 3 (oh crap) relays, K21 and K201, respectively, are in the box.

The overpressure relay, K22, is behind the glovebox.

[rf900rkw]

For the normal speed, Right hand cabin filter. Passenger side inside the DME electrical box.

For high speed, behind the glove box.

Stage 3, also in the DME box


e39-fan-relay1.jpg

[tscoll01]

Remember this is what is behind the fan after 100k milesphoto.JPG

[diddly]

Thanks again for the info. guys: Took a quick look at it a short time ago, to assess how to check the resistors: Can I get to them by removing the fan guard up front, or do I have to go much deeper, like remove the radiator and lean the AC condenser back, for access that way? I am of course hoping that it's just a bad resistor and it would be sweet (obviously) if there was a way to get at it through the fan. Now that I say all this; I suppose I should be checking the relays FIRST, since they are the most accessible! Also; just out of curiosity; that stage three relay, behind the glove box?; is that one and the same as 'the mysterious fuse number 75', that's listed on the fuse identifier card, (that I found in the owners manual), when actually, the highest numbered relay/fuse in the trunk, is #74?....That one puzzled me for a little while.

- - - Updated - - -

p.s. Thanks for the great pic and diagrams, rf: I'm saving them all, so that I can print them out and refer to them in the garage!

[diddly]

Finally got back to this car yesterday: Replaced that pesky little oil filter housing gasket, that was making such a mess. While out there; I checked the fan relays: Unfortunately; they were all fine! Sooo...how does one access those resistors? Can it be done from the front?

[SpeedsterBek]

Finally got back to this car yesterday: Replaced that pesky little oil filter housing gasket, that was making such a mess. While out there; I checked the fan relays: Unfortunately; they were all fine! Sooo...how does one access those resistors? Can it be done from the front?

You only need to pull the harness to check the resistors and low speed power.
Here is the harness you need to rotate and pull out (not my picture):
conn2.jpg

Harness will have 4 wires. Brown is ground, and others are low/med/high depending on wire thickness.

Turn on the car and A/C to check if there is power at the harness
To check the fan resistors, you can measure the resistance or just apply power the fan directly. You can grab some long wires and use power from top of the engine.

It is usually the low speed resistor that dies first, since A/C uses it. Here are some links to check out
http://www.bimmerfest.com/forums/sho...d.php?t=205728
http://www.laczik.org/BMW/repair/E38...8_aux_fan.html

You can replace the low speed resistor (I believe it's the 0.5 Ohm).

I had the low speed resistor blown. I just removed the faulty low speed resistor and bypassed it, so when A/C kicks in, my Aux fan runs at MEDIUM speed. I put fuse with a slightly higher amp rating too. No issues since last year. Do it at your own risk. My E39 is a spare beater car, so I don't care about it that much.

[diddly]

Wow; thanks man! After perusing the forum a bit more, I thought I found out that I HAD to remove the front bumper. I was just getting back on to the forum to say that I found that out, when I saw your reply. Cool; I'll try to make some time to attempt it this weekend. I know the medium speed is good. I think with a new low speed resistor, the system will be functioning as intended. After my mechanic set the Freon level last week; it was blowing coooold on the way home from the shop. Not sure if that fan was howling, (on medium speed) the whole way home though(?) It certainly may have been: It was over 100 degrees that day!

[diddly]

My enthusiasm is a bit 'curbed' this morning: I was so excited yesterday about not having to remove the bumper, just to replace a couple of resistors. Then it dawned at me: I can only TEST them without removing the bumper, right? I need to remove it, to REPLACE them!!! Duh! Oh well; I'm happy knowing the fan works and that I don't need one of those (a hopeful assumption, anyway). If the Germans were really crafty though; they would have put the resistors in a much more accessible spot!

[SpeedsterBek]

resistors are placed there to cool them off. They get very hot when the fan is turned on

[DHoang]

Questions: 1) Should this fan run on low speed as soon as AC is called for? And if not: When? (I'm assuming it's a 2-speed fan, as I can see a resistor mounted at the top of the fan.) 2) Is the fan controlled by a couple of different relays (i.e. one for each speed), that my owners manual says nothing about? 3) When SHOULD that fan run on high speed? (Does that 300 psi 'engagement point' seem reasonable/proper?

On my '98, the ac fan turns on anytime the compressor kicks on.The car could be stone cold in the morning, but if you have the ac on when you start up the motor, the ac fan kicks on as well.

The control of the variable fan speeds - WHEN AC is in use - is all done through the resistor pack. It's not done with relays.

Are you sure that the a/c fan is being triggered to come on based on 300 psi refrigerant load? Or could it be that concidentally, whenever you see 300 psi on the refrigerant gauge, it could also be that your coolant temp has exceeded 100c, and thus it's the coolant temp switch that's kicking on the ac fan? because it's my understanding that whenever one fan resistor fails, there's no longer any power going to ac fan that's associated w/ ac functionality. So even though your ac compressor pressure switch is telling the ac fan to kick on and off, the power has been cut off at the resistor. Do you understand what I'm trying to say here? You have to restore connectivity by either replacing one of the bad resistor, bypass one of the bad resistor, or even simpler, by pass both resistors, and thus the need to diagnose which resistor is bad is a moot issue. If you do the latter, then all you need to do is cut the wire going into the first resistor, cut the wire going out of the last resistor or resistor pack, and directly connect the two ends. Afterwards, the fan's circuit will be restored, and you should see the fan kick on whenever the ac is in use, but the fan speed will be at full rpm w/ resistor delete. This is a temporary fix (which if nothing else needs to be done asap before you trigger your compressor blow off valve to open and thus release refrigerant), and it could also be a permanent solution to these unreliable, short lived, resistors if you're a heavy ac user.

[ninetyseven1]

My enthusiasm is a bit 'curbed' this morning: I was so excited yesterday about not having to remove the bumper, just to replace a couple of resistors. Then it dawned at me: I can only TEST them without removing the bumper, right? I need to remove it, to REPLACE them!!! Duh! Oh well; I'm happy knowing the fan works and that I don't need one of those (a hopeful assumption, anyway). If the Germans were really crafty though; they would have put the resistors in a much more accessible spot!

You do not need to remove the bumper to replace the reisistors. Who told you that? un screw the aux fan cover on one side and push it out of the way. Move it down

[diddly]

On my '98, the ac fan turns on anytime the compressor kicks on.The car could be stone cold in the morning, but if you have the ac on when you start up the motor, the ac fan kicks on as well.

The control of the variable fan speeds - WHEN AC is in use - is all done through the resistor pack. It's not done with relays.

Are you sure that the a/c fan is being triggered to come on based on 300 psi refrigerant load? Or could it be that concidentally, whenever you see 300 psi on the refrigerant gauge, it could also be that your coolant temp has exceeded 100c, and thus it's the coolant temp switch that's kicking on the ac fan? because it's my understanding that whenever one fan resistor fails, there's no longer any power going to ac fan that's associated w/ ac functionality. So even though your ac compressor pressure switch is telling the ac fan to kick on and off, the power has been cut off at the resistor. Do you understand what I'm trying to say here? You have to restore connectivity by either replacing one of the bad resistor, bypass one of the bad resistor, or even simpler, by pass both resistors, and thus the need to diagnose which resistor is bad is a moot issue. If you do the latter, then all you need to do is cut the wire going into the first resistor, cut the wire going out of the last resistor or resistor pack, and directly connect the two ends. Afterwards, the fan's circuit will be restored, and you should see the fan kick on whenever the ac is in use, but the fan speed will be at full rpm w/ resistor delete. This is a temporary fix (which if nothing else needs to be done asap before you trigger your compressor blow off valve to open and thus release refrigerant), and it could also be a permanent solution to these unreliable, short lived, resistors if you're a heavy ac user.

I do believe I understand your explanation; which I commend you for expressing quite clearly! What I'm thinking after considering it, is this: When I observed the fan kick on at 300 psi, at the mechanic's shop, it sounded pretty robust, but I'm thinking not in the, "oh crap" mode. (Of course; I really can't say, since I have no real experience with this car. I've simply read enough posts saying that the fan sounds like a large airplane when that fan is 'in high gear': Mine only sounds like a small airplane ). If my assumption is correct; when I go out there to measure the resistors, I should find one of them (the .5 ohm one) to be 'open', correct? That assumes that the other resistor is controlling the fans normal speed, and the 'oh crap' mode is 'un-resisted'. I'm going out there right now to fart around with it: Afterall; it's Daddy's day! Thanks for the help! I'll let you know what I find out.


"You do not need to remove the bumper to replace the reisistors. Who told you that? un screw the aux fan cover on one side and push it out of the way. Move it down"

I guess I never read it explicitly: I just deduced it from all the threads I've read, dealing with auxillary fan failures. I hope I can figure out how to access it like you describe!

- - - Updated - - -

Actually; I'll take that back: I DID read it explicitly; in this thread: "E38 auxiliary fan slow speed resistor repair"

It starts out by showing you how to remove the bumper, before moving on to resistor repair/replacement!

- - - Updated - - -

On my '98, the ac fan turns on anytime the compressor kicks on.The car could be stone cold in the morning, but if you have the ac on when you start up the motor, the ac fan kicks on as well.

The control of the variable fan speeds - WHEN AC is in use - is all done through the resistor pack. It's not done with relays.

Are you sure that the a/c fan is being triggered to come on based on 300 psi refrigerant load? Or could it be that concidentally, whenever you see 300 psi on the refrigerant gauge, it could also be that your coolant temp has exceeded 100c, and thus it's the coolant temp switch that's kicking on the ac fan? because it's my understanding that whenever one fan resistor fails, there's no longer any power going to ac fan that's associated w/ ac functionality. So even though your ac compressor pressure switch is telling the ac fan to kick on and off, the power has been cut off at the resistor. Do you understand what I'm trying to say here? You have to restore connectivity by either replacing one of the bad resistor, bypass one of the bad resistor, or even simpler, by pass both resistors, and thus the need to diagnose which resistor is bad is a moot issue. If you do the latter, then all you need to do is cut the wire going into the first resistor, cut the wire going out of the last resistor or resistor pack, and directly connect the two ends. Afterwards, the fan's circuit will be restored, and you should see the fan kick on whenever the ac is in use, but the fan speed will be at full rpm w/ resistor delete. This is a temporary fix (which if nothing else needs to be done asap before you trigger your compressor blow off valve to open and thus release refrigerant), and it could also be a permanent solution to these unreliable, short lived, resistors if you're a heavy ac user.

I cannot say for certain, but I don't think that your understanding of the fan operation is totally correct: I THINK that even with the low speed resistor 'open', the fan will operate on MEDIUM speed (not "OH CRAP' speed). I believe this to be true, having just examined the wiring first hand and testing things with a DVM. SpeedsterBek talked about this a few replies earlier. I wound up doing almost exactly what he did: I removed the (dead) low speed resistor, and temporarily wired things so that when I hit the AC button on the control panel, the fan comes on at medium speed, instead of it's normally slower, low speed. I did not replace the fuse with a higher amperage one at this time! The only thing that I regret, now that I think of it, is that I did not bypass both of the resistors, just so I could see and hear what the fan is like at FULL SPEED. I can always do that when I install a new low speed resistor, I guess.
Oh, before I forget: I did make a couple of modifications to the car during this process. The first has to do with accessing the resistors without removing the front bumper. There is no way to get to the lower screw on the left side, that is holding the fan-guard in place: I drilled a small hole through the plastic 'shrouding', so that I could remove that screw. I figured a 5/16" hole in that plastic piece is not going to affect anything, and without it; you would need a screwdriver with 2 right angles on it, so that you could access a screw that's about 2-1/2" 'out of the picture'. The other mod was another small hole that I drilled right between the kidney openings, that let me put a screwdriver straight on to the LEFT screw, of the RIGHT resistor (as you're looking from the front). Without the hole I drilled, you're forced to come on to that screwhead at a significant angle; It's possible, but as those screws get rusty in a wet climate, the chances of stripping that tiny little Phillips head out is greatly increased. Now; I guess it's time to look for a new low speed resistor!
Thanks to all for their input on this; it sure made it clear on where to look and what to look for; plus, that temporary wiring idea from SpeedsterBek, came in handy (thanks man): I like the idea that a fan is on as soon as AC is called for! (Especially here in the desert!) I hope this thread is helpful to someone else with resistor issues.

[ninetyseven1]

It's not that complicated. '95-'98 cars have a three speed fan. '99 on have a computer controlled (PWM) fan. You have the three speed. Information on these fans is posted pretty much weekly. I posted up the wiring diagrams here.

http://forums.bimmerforums.com/forum...3#post27655843


To boil them down, again.

Normal speed any time the A/C is on, or radiator temp of 91.

Mid speed as a safety when A/C pressure exceeds 300psi

High speed is a oh crap at radiator temp of 104C




It would appear the normal speed circuit is blown. Fuse, relay, resistor. It's normally the resistor.

I just added a toggle switch by splicing into the blck/gray wire on the radiator sensor. It worked one time and now everytime i turn ignition on the fuse 7 blows! so i added a 30 amp fuse for testing purposes and now when ever i turn the key on the aux fan goes on high! this is without ac on. WTH is going on? where do i begin to start testing this thing? if i remove the low speed relay the fan stops, i removed the high speed relay first but fan kept running.

[Bmwe39528i1998]

Sorry to revive an old thread. 528i 1998/05.
Put a new Nissens aux fan 2 years ago.
Not working anymore. Pressing A/C button does nothing. Fan doesn't turn on at all, even if temp is past 110.
What's the best test?

[BimmerBreaker]

If you can't trigger it on in INPA, I would run a new signal wie for PWM, if that doesn't work, likely the fan is faulty

[JimLev]

Sorry to revive an old thread. 528i 1998/05.
Put a new Nissens aux fan 2 years ago.
Not working anymore. Pressing A/C button does nothing. Fan doesn't turn on at all, even if temp is past 110.
What's the best test?

Par for the course. I went thru 3 Nissens radiators in 9 months, then I bought a Zionsville.

[BimmerBreaker]

It's also a good idea to verify the ambient temp sensor is working. If it's broken the car thinks its -40 degrees and won't run the a/c