Blower only works on high

[jeffnhiscars]

Those points are what I've cleaned. On my first car I took out my multimeter and found that was where my problem was, did the quick clean with the 400grit and checked with the meter. Everytime I run into that problem I just clean and go.

Glad you have all 4 speeds back.

Until I actually had the resistor in my hands I was not aware of the points so I thought all this talk about cleaning contacts referred to the 4 in line terminals that plug in to the motor. No wonder it made no sense to me ..lol

[fronton]

thanks guys, I guess I'm hosed and will have to drop the engine after all. Too bad I don't have an engine crane any more :(

[Quadrajet]

Those points are what I've cleaned. On my first car I took out my multimeter and found that was where my problem was, did the quick clean with the 400grit and checked with the meter. Everytime I run into that problem I just clean and go.

Glad you have all 4 speeds back.

[Todd Black 88]

Chaps, I indeed cannot get my blower's firewall cover off without dropping the engine so at this point, pulling the dash is easier. Is someone certain that I'll have easy access to the resistor pack with the dash out?

My problem is the same as OP, blower works only on 4.

Jeff, I'm not sure why, it could be the design of the resistor pack. All I know is that it's common for only 1-3 to stop working all at once.

Fronton, engine swap huh? I think I would rather lower the engine than remove the dash and hvac unit JUST to get the blower motor out. That's crazy. The blower is designed to be accessed from the engine compartment. Use it as an excuse to drop the engine and do maintenance work or something. Put in a new blower and resurface the resistor contacts (or get a new one) while you're at it because you don't want to have to get back in there again for a long, long time.

To answer your question, pulling the dash is just the first step. You would then have to remove the entire HVAC unit from the firewall. Then you can get to the blower from inside the car.

And....... The nuts that hold the hvac box are on the engine side of the firewall.
Gonna have to drop the motor unfortunately.

[jeffnhiscars]

Jeff, I'm not sure why, it could be the design of the resistor pack. All I know is that it's common for only 1-3 to stop working all at once.

My new resistor did restore all 4 speeds and its good that I had it on hand as I snapped the frame on the brittle old resistor while removing it. I'm looking at one that came on an HVAC unit I was given and there are only 3 coils, so for sure you are correct that high speed is straight through (or so it would seem). What I think we have missed though is that there is a set of points that appear to bridge the second terminal from the left (looking from the rear) to one side of the heavy coil at the bottom.

We know points are a weak point in any circuit so it would be interesting to cross check a wiring diagram to see how the points come in to play.

[reelizmpro]

Jeff, I'm not sure why, it could be the design of the resistor pack. All I know is that it's common for only 1-3 to stop working all at once.

Fronton, engine swap huh? I think I would rather lower the engine than remove the dash and hvac unit JUST to get the blower motor out. That's crazy. The blower is designed to be accessed from the engine compartment. Use it as an excuse to drop the engine and do maintenance work or something. Put in a new blower and resurface the resistor contacts (or get a new one) while you're at it because you don't want to have to get back in there again for a long, long time.

To answer your question, pulling the dash is just the first step. You would then have to remove the entire HVAC unit from the firewall. Then you can get to the blower from inside the car.

[fronton]

Chaps, I indeed cannot get my blower's firewall cover off without dropping the engine so at this point, pulling the dash is easier. Is someone certain that I'll have easy access to the resistor pack with the dash out?

My problem is the same as OP, blower works only on 4.

[jeffnhiscars]

I just shoot crows myself;)

I've done the clean and replace on 3 or 4 BMW's now. Not to say your's couldn't be blown, if it is, then maybe it's been cleaned 4 times already.

I believe after the 2nd cleaning they get smashed with a hammer....and it's a noble man indeed who shoots his own crow....before it's served to him

That's my other point...it cannot be blown. It's just solid state coils! It'll work provided the circuit isn't open and the contacts make a good connection. It's not a traditional resistor pack like the aux fan resistor.

As for why it works on 4 and not any of the lower speeds...this is my theory:

Ohms Law : i=v/r

We see that current decreases as resistance increases. Max speed position 4 has virtually no resistance therefore you have max current, position 3 has a little resistance, position 2 has a little more resistance and position 1 has even more resistance since position 0 is just off (infinite resistance). When you have an old motor with worn brushes it may take more current to kick on. From what I've seen, max current position 4 is usually enough current to start the motor while the lower speeds cannot. My guess is they don't provide enough current to break the oxidation threshold. I would even venture to say that if people left it alone and didn't fix it, max speed position 4 will eventually stop working over time.

Thats a reasonable theory...however (there's always a "however" isnt there) based on what you say the problem should be progressive depending on the relative stage of the oxidation threshold (OT) in conjunction with the resistance of each speed. You seem to agree with the progresive notion (and its logical) when you "venture to say...speed 4 will stop eventually".

Since I have not seen a post saying "my fan only works on 2-4", why do speeds 1-3 seem to go out at the same time when they should each have the same OT at any given moment and should by all rights require different OT's to stop ?

[reelizmpro]

That's my other point...it cannot be blown. It's just solid state coils! It'll work provided the circuit isn't open and the contacts make a good connection. It's not a traditional resistor pack like the aux fan resistor.

As for why it works on 4 and not any of the lower speeds...this is my theory:

Ohms Law : i=v/r

We see that current decreases as resistance increases. Max speed position 4 has virtually no resistance therefore you have max current, position 3 has a little resistance, position 2 has a little more resistance and position 1 has even more resistance since position 0 is just off (infinite resistance). When you have an old motor with worn brushes it may take more current to kick on. From what I've seen, max current position 4 is usually enough current to start the motor while the lower speeds cannot. My guess is they don't provide enough current to break the oxidation threshold. I would even venture to say that if people left it alone and didn't fix it, max speed position 4 will eventually stop working over time.

[Quadrajet]

I just shoot crows myself;)

I've done the clean and replace on 3 or 4 BMW's now. Not to say your's couldn't be blown, if it is, then maybe it's been cleaned 4 times already.

[jeffnhiscars]

I misread what you were saying in your post last night. I was reading off and on from my phone while at work. You didn't have to buy another resistor is my point just resurface the contacts. It's worked for me for several years. Sure a new board will fix it (if the motor isn't on the way out too) but not because the old one is "bad." I felt that oxidation was a more accurate description because the contacts look fine when you remove the pack. It would help to spray some contact cleaner in the motor before installing the board. Goodluck.

It's so ridiculously simple to do what reeliz is suggesting. I took some 400grit wet or dry, folded it over and dragged it thru the contacts like 3 or 4 times and was done. Of course it took way more time to get to the unit and reassemble it again.

Barry I often misread the 32nd post in a thread so I understand.

I have no problem servicing anything and in some cases will fix things that arent intended to be fixed. I've done enough speedo gears & window switches etc etc. In this case I took the lazy route and did not fully explore the blower resistor mostly cause it made sense to me that it was blown since with 4 speeds it seemed unllikely that the same 3 contacts (1-3) would oxidize in a number of cases while 4 always remained working.

I also thought since I do have to take the damn thing out regardless, I may as well have the replacement on hand. Besides the free shipping, curiosity came in to play as this is probably one of the few parts I have never touched on an e30..lol

When I get it out I will surely clean it and if it works Ill have a new spare for when one of the 3 other e30's in the driveway needs one (well really 2 since the 84 318i only has a 3 spd ).

IF, however, the resistor is blown, how do you guys like your crow served ? :giggle:

[reelizmpro]

This is one of those things where...you can fix the part but shops typically will just replace it. For shops it makes more sense to simply sell and replace the resistor or entire blower motor for that matter. But for the BMW DIY owner who knows how to do the job, it's worthwhile to clean the contacts and save their money. They may need it for another blower motor later when the brushes go bad.

[Quadrajet]

It's so ridiculously simple to do what reeliz is suggesting. I took some 400grit wet or dry, folded it over and dragged it thru the contacts like 3 or 4 times and was done. Of course it took way more time to get to the unit and reassemble it again.

[reelizmpro]

I misread what you were saying in your post last night. I was reading off and on from my phone while at work. You didn't have to buy another resistor is my point just resurface the contacts. It's worked for me for several years. Sure a new board will fix it (if the motor isn't on the way out too) but not because the old one is "bad." I felt that oxidation was a more accurate description because the contacts look fine when you remove the pack. It would help to spray some contact cleaner in the motor before installing the board. Goodluck.

[jeffnhiscars]

Why do u think there is a resistor pack in the first place? Think about it. Max speed is straight through, no resistance because its just ON. A new board will solve your problem but it woulda been a simple fix. Corrosion wasn't a good term, its more like oxidation.

I'm not sure I see your point or what you mean by "it would have been a simple fix"

Here's the realoem diagram showing the resistor as #5 so it certainly exists in at least some applications and this particular diagram is based on my VIN.

http://www.realoem.com/bmw/showparts...19&hg=64&fg=35

As to the corrosion\oxidation point, I try to keep my terms similar to the post Im responding to keep it easier to follow the train of thought. The fact is, that while corrosion is the result of a chemical reaction, oxidation is considered a form of corrosion, although obviously with oxygen vs some other chemical so they are reasonably interchangeable in this conversation.

Something steps down the amperage to create different fan speeds. Its either in the switch or via a separate device, much the same as with the aux fan resistor. Having read more than one thread about a "high speed only" blower being fixed by a new resistor (or resistor pack if you prefer), I ordered one on spec since I was ordering a hood and trunk strut to keep them from falling on my head and they werent enough to get me free shipping.

Not sure if this addresses your point but its early so maybe Im just blathering :)