Aux fan in-line diode replacement

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blockerb
Posts: 127
Joined: Apr 28, 2011 9:58 AM

Aux fan in-line diode replacement

Post by blockerb »

1986 528e all factory

any recommendations for replacing the auxillary fan in line diode. My aux fan is not coming on when pressing the "snowflake" button. Searched all over the forum and google and can't seem to find anything about replacing it and where to get an appropriate part. researched the ETM and have done the following:

press snowflake button and lights up blue
compressor clutch engages
no aux fan.

-replaced resistor on the fan
-tested the aux fan by jumping low speed switch connectors and high speed switch connectors at the radiator. Fan works in both scenarios. which tells me the fan is good, the radiator switch is good, the relays are good, and the fuses are good. this is based on the ETM diagrams for 1986 528e.
-Becauase the compressor clutch engages when i turn on the AC/snowflake button, i can deduce that the high pressure switch is working as expected and is not th problem.
-Based on the ETM, this leaves on the in-line diode from the compressor to be the failure point. I've located it at the passenger side as part of the wiring behind the passenger side headlight.

I can't seem to find any info about the specs of this diode and can't even located a similar diode with the same form factor. Seacher ecs tuning, pelican parts, and fcp euro, and YES seached all over mye28.com and found some references to this part but nothing conclusive and certainly nothing about sourcing a suitable replacement.

to test voltage to the aux fan with the AC button turned on, i assume i can connect the postive lead of my multi-meter to the first connector on the resistor (the one with only one wire connected to it, i.e. the low speed connection) and connect the the ground lead to the negative battery terminal and should get a voltage reading? If ture and i don't get a voltage reading....

1. Am i missing something?
2. Where can i find a suitable in-line diode replacement?
Mike W.
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Joined: Feb 12, 2006 12:00 PM
Location: California Whine Country

Re: Aux fan in-line diode replacement

Post by Mike W. »

blockerb wrote: May 23, 2023 10:08 PM 1986 528e all factory


to test voltage to the aux fan with the AC button turned on, i assume i can connect the postive lead of my multi-meter to the first connector on the resistor (the one with only one wire connected to it, i.e. the low speed connection) and connect the the ground lead to the negative battery terminal and should get a voltage reading? If ture and i don't get a voltage reading....
For a non electronics guy, you're doing pretty good, but no. The input from the A/C compressor goes to the low speed relay coil, not directly to the fan. It turns on the relay which in turn, turns on the fan. So technically you would check for voltage at the 86 terminal of the low speed fan relay. I can't remember, but it seems like on E28s the diode might be in a little plastic housing which you can just unplug, in which case do so and check for resistance/continuity.

1. Am i missing something?
2. Where can i find a suitable in-line diode replacement?
Basic switching diodes like this are very non specific. I want to think for some reason they're in the 1N4xxx series, which is a very common one amp diode available in a wide variety of voltages. Just get a generic one off amazon, if you want overkill get a 3 amp or a 5 amp or something, probably 50 volts rating. Just insulate it well and don't overheat it if you solder terminals on it, do it quickly. You do not want a Zener diode, but beyond that it's pretty wide open. Get cheap, not fancy.
gadget73
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Joined: Nov 22, 2017 10:30 PM
Location: New Jersey

Re: Aux fan in-line diode replacement

Post by gadget73 »

I might suggest a 3 amp if for no better reason than you generally get fatter leads to work with than a 1 amp diode.
blockerb
Posts: 127
Joined: Apr 28, 2011 9:58 AM

Re: Aux fan in-line diode replacement

Post by blockerb »

Thanks. I'll test out the diode and verify that's it. Don't know what else it could be. Once i source a replacement, I'll follow-up with the result.
blockerb
Posts: 127
Joined: Apr 28, 2011 9:58 AM

Re: Aux fan in-line diode replacement

Post by blockerb »

Update ...

Found this on ECStuning.com

https://www.ecstuning.com/b-genuine-bmw ... 311358265/

looks slight different shape and doesn't specify amperage, but it has the male and female spade terminals like the existing one, and it sounds like generally, diodes are non-specific, so will try it and see if it works.

Mfg Part #
61311358265
61-31-1-358-265
61 31 1 358 265
61.31.1.358.265

ECS Part #
ES#2706804
Mike W.
Posts: 26872
Joined: Feb 12, 2006 12:00 PM
Location: California Whine Country

Re: Aux fan in-line diode replacement

Post by Mike W. »

Relatively expensive, but the convenience factor may be worth it. Looks like it should work.
blockerb
Posts: 127
Joined: Apr 28, 2011 9:58 AM

Re: Aux fan in-line diode replacement

Post by blockerb »

Alright so here's the update. Searched for, and found the diode behind the passenger side headlight on one of the wiring harnesses. removed the rubber protective wrap on it and disconnected to take a loot at it and then reconnected. Ordered the new part. While I was waiting on the new diode, i went ahead and recharged the system. There was no refrigerant in the system up to this point. Once I recharged and ran started and tuned on the AC to test. The aux fan came right on when i pushed the AC button. So not sure what happened, maybe disconnecting and reconnecting the diode did something. not sure. so, so far seems to have been resolved.

Thanks.
Galahad
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Re: Aux fan in-line diode replacement

Post by Galahad »

blockerb wrote: May 31, 2023 10:22 AM ... So not sure what happened, maybe disconnecting and reconnecting the diode did something. not sure. ...
That can happen, plugging stuff back in tends to wipe off corrosion from the contact surfaces
1st 5er
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Re: Aux fan in-line diode replacement

Post by 1st 5er »

blockerb wrote: May 31, 2023 10:22 AM Alright so here's the update. Searched for, and found the diode behind the passenger side headlight on one of the wiring harnesses. removed the rubber protective wrap on it and disconnected to take a loot at it and then reconnected. Ordered the new part. While I was waiting on the new diode, i went ahead and recharged the system. There was no refrigerant in the system up to this point. Once I recharged and ran started and tuned on the AC to test. The aux fan came right on when i pushed the AC button. So not sure what happened, maybe disconnecting and reconnecting the diode did something. not sure. so, so far seems to have been resolved.

Thanks.
Wondering if the aux fan doesn't get a signal to come on if the compressor isn't compressing. 🤔
Mike W.
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Joined: Feb 12, 2006 12:00 PM
Location: California Whine Country

Re: Aux fan in-line diode replacement

Post by Mike W. »

1st 5er wrote: May 31, 2023 8:57 PM

Wondering if the aux fan doesn't get a signal to come on if the compressor isn't compressing. 🤔
It should get a signal if the compressor is running, but doing any work or not shouldn't matter. E28s don't have a low side switch like most cars, so the compressor should run if the switch is on, regardless of charge.
1st 5er
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Re: Aux fan in-line diode replacement

Post by 1st 5er »

Mike W. wrote: Jun 01, 2023 12:09 AM
1st 5er wrote: May 31, 2023 8:57 PM

Wondering if the aux fan doesn't get a signal to come on if the compressor isn't compressing. 🤔
It should get a signal if the compressor is running, but doing any work or not shouldn't matter. E28s don't have a low side switch like most cars, so the compressor should run if the switch is on, regardless of charge.
👌
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