Blower only works on high

[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 ?

[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.

[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.

[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.

[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.

[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.

[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 :(

[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