Cold-weather FSU problems? Try dielectric grease.

[geargrinder]

TL;DR tip for FSU problems when you know your FSU and blower are both good, and it only acts up in extreme temperatures: try a little dielectric grease on the connector.

Long story: So like most of us who live in high-blower-motor-use geographies, my FSU crapped out eventually a few years ago.

I also went through a couple - definitely went through a used one that was assured had been tested running perfect but didn't work at all. Then had a new one that crapped out over a short time. When I got a 2nd or 3rd replacement or something (thanks for dealer-part and FCP warranties by the way!) and found it seemed to be acting up again, I decided to look a bit further, and identified that indeed seemed like my plug pin sockets maybe had loosened up, as I could sometimes wiggle the connector and get the FSU working again. I'd tried lots of connector wiggling before so definitely some FSU failures occurred but it seemed like I was facing a 'dual failure mode' situation...

I was dreading trying to re-pin the connector sockets in the FSU pigtail behind the dash (how you'd crimp all the wires up under there with quality crimps I can't imagine...) and so I tried to tweak my connector sockets a bit w/ a pick to tighten them up again, and in fact yes, that worked great, and I had no FSU problems for a few years (replaced the blower motor twice but that was a whole different set of stories! probably should have repinned the damn connector when the whole dash was out now that I think of it!)

Well this winter comes on, and, suddenly, with new blower in the dash and the relatively recent FSU, I find that at super cold temps, the blower was again doing the 'failed FSU' type symptoms. Get the bars on the climate control, thinks its working, but its not. Sometimes when the car warms up suddenly the blower would come on, sometimes it would never return.

Thinking back about my connector woes, I pulled the plug, dipped my tender fingertip in sweet silky loob, and smeared some up on the FSU pins and a lighter schmear on the connector side socket holes (don't want it to be a crazy KY mess in there, just a little smidge to coat the pins). Just the usual dielectric grease you can buy from any FLAPS.

Voila (don't ever say "Walla", that is for retards and peasants), ever since, from sub-zero F temps to 50+ degrees, blower has been working perfectly. Clearly some micro corrosion and/or temp warping to the parts was happening to limit the signal through the connector just enough to stop it from working.

Worth a try if your FSU and blower are known good and you suspect maybe a hinky connection. Definitely does NOT preclude the FSU from crapping out tho'. Those things blow.

[edjack]

What's a "FLAPS?"

[geargrinder]

Dated car forum abbrev: Friendly Local Auto Parts Store

[edjack]

Journalistic practice urges that, the first time one uses an acronym, he/she defines it, unless it is in common usage, and well-known by the intended audience.

[computiNATEor]

Haha, gonna have to remeber FLAPS.

I've owned 3 E39s with more than 100,000 miles driven by me. I've never had the misfortune to experience an FSU failure.

[6spd540]

Mine works fine when it's cold (well as cold as it gets here), actually it might not since it doesn't ever need to blow very high. The couple of times I've needed to hit the front defrost button it has kicked up to high.

In the summer if it's one of the normally hot days (high of 95) or heat wave hot it won't blow on high until the car cools down a bit. Ironically right around the time it kicks into high is when it starts to slow down. The rest of the year when the high is 75-85 at the times it calls for high blower it seems to work but the car is only about as hot as when it kicks in on the hotter days.

I haven't even bothered with trying to fix it since the still cools off just as fast if not faster than the rest of our cars. When I first noticed I figured it was the FSU and would just change it when it fails completely and it would probably be soon (that was about a decade ago).



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[f355spider]

I'm not sure the grease is helping. What is more likely fixing the problem is removing and reinstalling is "renewing" the connection contacts. Understand that the grease does not enhance the connection, it is simply sealing out dirt and moisture from contaminating the connection. Regardless, it fixed your problem, so kudos.

[geargrinder]

I'm not sure the grease is helping. What is more likely fixing the problem is removing and reinstalling is "renewing" the connection contacts. Understand that the grease does not enhance the connection, it is simply sealing out dirt and moisture from contaminating the connection. Regardless, it fixed your problem, so kudos.

Nope. Yeah I know how dielectric grease works. It’s not a conductor etc. missing a lot of what I said I think.

No, jiggling the connector alone wasn’t a permanent solution, it might work once or twice but was fiddley. Note this isn’t for a non working FSU situation. This is... well hell just read what I said already, you might have missed it. What the dielectric does is keep the connector from losing its working connection when it flexes from temp It DEFINITELY is what made the difference. I had even tried magic Deoxit befor without luck which is more of a “connection restorative”.

[f355spider]

Nope. Yeah I know how dielectric grease works. It’s not a conductor etc. missing a lot of what I said I think.

No, jiggling the connector alone wasn’t a permanent solution, it might work once or twice but was fiddley. Note this isn’t for a non working FSU situation. This is... well hell just read what I said already, you might have missed it. What the dielectric does is keep the connector from losing its working connection when it flexes from temp It DEFINITELY is what made the difference. I had even tried magic Deoxit befor without luck which is more of a “connection restorative”.

I get what you are saying now....the grease is holding the pins steady from moving via temperature changes? Sure, that makes sense.

I agree with your findings on Deoxit. Not a fan of those connection "enhancers" I tried Stabilant 22 back in the day and had mixed results...I think the stuff just gums up the connection more in reality. "clean and dry" is my motto now.

[geargrinder]

Actually I’m a huge fan of deoxit a lot of the time but this is one of those situations that it proved to be not the right tool. Gotta have a few tricks in the toolbox for stuff like this!

[BimmerHoop]

I'm not sure the grease is helping. What is more likely fixing the problem is removing and reinstalling is "renewing" the connection contacts. Understand that the grease does not enhance the connection, it is simply sealing out dirt and moisture from contaminating the connection. Regardless, it fixed your problem, so kudos.

I've had the blower inop issue for a while off and on. Confirmed good blower by jumpering the connector, ohmed out the FSU, checked voltage from IHKA panel, bought a new FSU (Hella/Behr Chinese vs original Valeo German, ohms out identical to Valeo unit), tried dielectric grease too. Symptoms are blower just stops working at all, after working for weeks or years. Manifests in summertime, so no A/C, NOT GOOD in Alabama.

Latest fix is to use a pick tool to squeeze/deform the five sockets inside the female connector slightly to make oval shaped, for more positive contact with the FSU pins. It works again, at all speed settings on the IHKA.

My theory is that as the blower motor ages, it pulls more current, FSU gets hotter, connector expands/shrinks and oxidizes until good contact is lost. I've also tried to lube the blower motor to stop the chirping, went in through the firewall, and discovered it moves but does not spin freely, not sure if this is normal or not since I don't have a new blower. But that's why I surmise my motor may be pulling more current. Maybe that doesn't contribute to the problem, maybe it's just 17 years of normal temperature cycling on the connector. I usually set the blower on a lower setting, in an attempt to save the motor, but that may be putting more stress on the FSU and connector.

One more interesting note (depending on your personal threshold for amusement) is that the first time I tried to fix this several years ago, I bought the Hella FSU. Didn't work, thought I got a dud, put the old one back in and it worked (for a few years). Didn't question why, just happy to have A/C back, and tossed the Hella FSU in a drawer. I suspect many of the apparent FSU problems are actually just connector issues, solved by putting an FSU with fresh pins in.

So my advice to anyone just starting to attack the problem is to:
1) Check your blower motor by jumpering pins 2 to 5, and 1 to 4, with some 12 ga wire on the FSU connector (Can get big sparks, might want to use a long wire for 1-4 and go instead from 1 to some bare metal on the chassis as the last thing you connect). Should blow full speed, even with ignition off.

2) Test the speed control voltage from the IHKA by measuring volts between pin 3 and chassis ground. Should vary between 2 to 8VDC at speed settings from 1 to 16 bars on the IHKA.

3) Use a pick tool to deform the female sockets on the connector slightly, just enough to improve contact, but still allow connector to seat. Apply some dialectric grease too, can't hurt, may protect it in the long run.

4) If still no joy confirm pin 4 in connector is grounded to chassis (long shot)

Crude connector pin diagram:
_____
/ 5 4 |_
/ 3 2 1 |
-----------

If you want to ohm out your FSU, put one probe firmly on the "hedgehog" cooling tines with other probe to:

Description-------Pin--kOhms (nominal values, expect a little variation*)
______________________________
Blower Ground---1----~0
12V from relay --2--1200
IHKA speed ------3---600
Chassis Ground --4---600
Volts to blower ---5--1200

*One website had the values on 4 and 5 higher, ~2 megohms to 3 megohms for a new unit, but mine both read the same as in the table above, old and new.

If all that checks out and STILL no luck, then maybe your blower motor has worn out brushes that only respond to instant full 12 volts that comes from jumpering the connector. Next step, the dreaded dashboard teardown to replace the motor!!

[Apologies to all those whose info I used, I've been researching this for a while and the above is a mashup from many different posts and youtube videos]



UPDATE 10/7/2019
Some time after posting the above in June, the unit started to act up again, ie fan would not work, had to reseat the FSU and then it would run for a while. THEN, NEW SYMPTOM, the fan would not shut off even after turning off the car. Replaced the original FSU with the Hella unit I'd bought a while back, and since then have had no problems. That was at least a month ago.

So, I think I had two failure modes going on: 1) poor connection at the FSU, helped by tightening the connector sockets, and 2) failing FSU

Who knows, maybe it was the FSU all along, but when I first tried the new Hella FSU a couple years ago, it did not work either. It was only after tightening the connector sockets with the new FSU that the problem apparently was fixed, so I can only conclude the connector sockets were part of the problem.

One other note: the fan used to chirp a little at low speed, before I dabbed a little grease on the shaft/bearing that I could reach through the cabin air intake through the firewall (not easy). I know, it's a sealed bearing, but I though it couldn't hurt, and the fan has stopped chirping. Coincidence? Maybe just enough grease migrated into the bearing to help?


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2002 530i Msport 5-spd
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[Santaclaus4]

I realize this may seem counter intuitive but turining the fan speed down actually puts more strain on the motor and FSU. They both work the least when at full speed.
The FSU can not turn the fan speed up, only less down.
At full speed, the FSU isn't really doing anything but passing current around the circuit instead of through the resistors so it's not generating any heat inside it's housing.
Higher current passes through bad connections better than low current, or just finds an easier path to ground anyway...

[jicaino]

(yadda yadda blah blah) Voila (don't ever say "Walla", that is for retards and peasants) (yadda blah)

Kind sire, thee may want to start using a dab of dielectric grease everywhere you replace or remove-reinstall a plug, pin, relay, bulb or component. Only retards and peasants fail to do so.

[Kirk Anderson]

No temp extremes needed. My blower just refused to come on today. Used BimmerHoop's excellent post to jump the blower motor. Whirrr whirrr. Also checked resistances on the FSU per same post and they looked right. Put some conductive grease (not dielectric) on the pins, plugged it back in. Done (for now).

I think that took me three hours. Next time: 60 minutes.