Aux fan troubleshooting

[fiveightandten]

1986 325es. All stock M20B27. My aux fan doesn't seem to be working. I'm looking for some help to troubleshoot it. Here's some info:

-Brand new 91º and 99ºC switches installed.
-Both switches are getting voltage.
-T-stat is opening fine
-Fan kicks on when I jump the 99ºC (high) switch.
-Fan does NOT kick on when I jump the 91ºC (low) switch.
-Fan does NOT kick on when I turn the AC on.
-I have not replaced the low speed resistor, but all the connections are intact.
-I swapped the relay for another one of the same type in the distribution box. No change.
-All fuses have continuity, and are definitely not blown. They have voltage on them.

I let the car idle and the temp gauge will get up to the 3/4 mark without the fan kicking on. The mechanical fan won't let it get any hotter than that. But I feel like this aux fan should be kicking on at that point. Are early models supposed to kick the fan on when the AC is engaged?

Any input? Thanks in advance.

[TurboJake]

Are early models supposed to kick the fan on when the AC is engaged?

Yes, they are. But the thing you haven't replaced... and admitting to not having replaced it... Is the thing you need to replace.

[fiveightandten]

Yes, they are. But the thing you haven't replaced... and admitting to not having replaced it... Is the thing you need to replace.

Thanks. I found PN 17401373177 on RealOEM, but some websites (ECS, for instance) are listing this as the blower motor resistor for the CC.

Can you/anyone confirm the aux fan resistor PN for an early model ETA?

[dsphil]

If you replace the resistor and still doesn't work, check the c113 connector behind the driver side headlights. the bk and bk/gn wires maybe not connected or broken like my did.

[fiveightandten]

If you replace the resistor and still doesn't work, check the c113 connector behind the driver side headlights. the bk and bk/gn wires maybe not connected or broken like my did.

Cool, thanks for the tip.

[TurboJake]

Thanks. I found PN 17401373177 on RealOEM, but some websites (ECS, for instance) are listing this as the blower motor resistor for the CC.

Can you/anyone confirm the aux fan resistor PN for an early model ETA?

Yep, that's the resistor you need.

Looks like this.




The blower motor resistor pack looks like:


And is part number 64111468521. Not even in the ballpark. ECS totally has the wrong description.

:up:

[mpowerful]

Stolen from a post by richardodn at bimmerforums. It is comprehensive.

Troubleshooting the aux fan.

1. Pull the K1 (normal speed) and K6 (high speed) fan relays from the fuse box.
2. Check for voltage on socket pin 30. It should be hot at all times.
3. Turn the ignition to run and check for voltage on both sides of fuses 19 and 20. The voltage should be essentially the same on both sides of the fuse. If not, replace the fuse.
4. Jump the wires on the radiator temp switches.
If you have 2 switches:
a. Jump the normal speed switch, green/black to black and check for voltage at socket pin 85 of the K1 relay. It should read 12V with the ignition in run.
b. Jump the high speed switch, green/black to black/brown and check for voltage at socket pin 86 of the K6 relay. It should read 12V with the ignition in run.
If you have the dual switch:
The wire colors are the same. You just need to jump them in the 3 pole connector. Pin assignments are as viewed from the connector face.
Pin 1 (across from flat side) should be green/black
Pin 2 (across from key) should be black
Pin 3 (remaining) should be black/brown
5. Replace the relays and redo the temp switch tests. The fan should come on in normal and high speeds.

If high speed does not come on:
With the aux fan high temp (green/black to black/brown) switch jumped, check for voltage on both sides of fuse 18. If you have no voltage, the K6 relay is suspect. If there is any appreciable difference across the fuse, replace the fuse. Check for voltage at aux fan on the red wire. If you have no voltage, there is a wiring fault. If you have voltage, the fan or ground is suspect.

If low speed does not come on:
With the aux fan low temp (green/black to black) switch jumped, check for voltage on both sides of fuse 3. If you have no voltage, the K1 relay is suspect. If there is any appreciable difference across the fuse, replace the fuse. Check for voltage at aux fan resistor on the black wire. If you have no voltage, there is a wiring fault. If you have voltage, check for voltage on the aux fan red wire. It should be less than 12V. If you have voltage, the fan or ground is suspect.

Finally, we need to check that the AC can engage the normal speed fan.
Remove the K1 relay. Turn the AC on and test for voltage on socket pin 86. If there is no voltage, then there is an HVAC problem.

[jlevie]

If the temp gauge goes above 1/2 when idling with the AC off, you have other problems. Which could include a bad fan clutch, bad thermostat, clogged radiator. That needs to be dealt with before worrying about the aux fan.

[95BMWIC]

I had same issue - I replaced the resistor with a new one this Spring.

My resistor is different than the pic above.

I used a 64121388069 ACM resistor and now everthing works great - Ordered it from AutohausAZ..

[fiveightandten]

Thanks for the info everyone. I ordered a resistor, which came in today. Despite zero visible corrosion, I had to drill the mounting screws out. They were positively frozen in place. Anyways, the new one is in, and the fan is now working as it should.

As a side note, this thing gets HOT. Is it normal for it to be scalding hot after the fan was only running for a minute or 2 (on low as a result of the AC being engaged)?

[jeffnhiscars]

For future reference , if the aux fan does not kick on when the AC is engaged first thing to do is jump the resistor. 98.4% of the time that will solve it.

[z122643]

So I have a similar issue with my AUX fan. I just replaced it w/ resistor all new. It blows the fuse instantly when engaged. I've traced the wires completely. No breaks, no crosses, and no damaged wires.

Ideas?

[fiveightandten]

So I have a similar issue with my AUX fan. I just replaced it w/ resistor all new. It blows the fuse instantly when engaged. I've traced the wires completely. No breaks, no crosses, and no damaged wires.

Ideas?

Does the fan spin freely by hand?

Are you sure the wires are connected to the resistor properly? 2 on one side, 1 on the other. I don't have it in front of me to tell you what goes where. But I can look.

I'd disconnect the wires from the resistor and jump the high speed switch. See if it blows the fuse that way. If it doesn't, you know it's an issue with the low speed wiring through the resistor. If it blows in either condition, I'd start checking for shorts at the fan or distribution box.

[ahlem]

What happens if there is no ground circuit from the K1 resistor activating circuit when tested with a multimeter checking continuity from the female terminal to the car body?
C113 ground suspected? I'd prefer not to have to take the fuse box apart.

[ahlem]

Everyone stumped on this question?