Car question (fan motor)

Factual Questions
1

I have a 2003 BMW 3-series.

Today, i started it up and pushed the A/C button as I normally would, but no air came out of the ducts. “Uh oh,” I thought. “The A/C is dead and I probably need a new compressor.”

So , I rolled the windows down, and started on my way. About 30 seconds into the trip, the fan kicked on, and cold air came out of the vents. Woo hoo! It is working!

But before I was able to enjoy the moment, the fan died again. For the rest of the trip, the fan cut in and out, and also ran at different speeds. I turned the A/C off, and the fan operated exactly the same, only when it worked, the air was not cooled like it was with the A/C on.

So, I figure i have a fan issue. But what should i look for? The car has not had one electrical issue since I’ve owned it, so could the fan be dying on its own, without any sort of electrical issue playing a part? Or is there a clutch in the fan and the clutch is slipping?

I don’t know much about fans (obviously) so I thought i’d ask the car folks out here.

Where should I start looking?

  1. I ruled out the fuse because as I understand the electrical system, if the fuse blew, the fan wouldn’t work period.

  2. The A/C still works and blows nice and cold, so the A/C compressor is ok.

  3. is there a belt that could be slipping? Or is this fan purely electrical?

Thanks for any help!

2

I would almost bet that you have a burned plug connection at the fan or possibly a loose ground.

3

It could just be a bad resistor. What are you driving? Are you handy? Do you have a multimeter?

I’m going to guess you need a new resistor, though these aren’t exactly the classic symptoms of the resistor burning out. Wasn’t it doing anything funky before, like only one or two of the speeds working or all of the speeds blowing the same?

Without knowing the answers to these, here’s my generic advice. Crawl under the dash on the passenger side (remember, generic advice). The blower motor should/might be under there. It’ll be a barrel shaped thing with some wires screwed into it. Unscrew the screws or unclip the clip and pull the wires. Start the car, turn on the fan, check for voltage. Got voltage? If you do, you probably need a resistor. Easy fix, you’re halfway there already, it’ll probably be about $40. No voltage, you’ll have more work on your hands.

4

I have no idea what’s actually in your BMW. Maybe one of our resident car experts can help with that. What I can tell you is that on most cars, the fan is a fairly simple thing. The switch will have several positions on it (off, low, med, hi) and the wiring from here goes to a resistor pack. Low and medium will put resistors in series with the fan to slow it down. High will make a straight through connection to the fan so that it runs at full speed. Often when the resistor pack starts to go, low and medium may not work properly but high will work fine.

You have an intermittent connection somewhere. It could be in the switch. It could be in the resistor pack. Or it could be in the fan itself, or just in the connector that attaches to the fan. Or maybe a critter chewed part of your wiring or the wiring chaffed on a sharp piece of metal somewhere.

If you are handy with a multimeter, you can track this down fairly easily. Put the meter on the fan terminals (might be a bit difficult to access depending on the design of your car) and turn the fan on. If the fan receives a constant voltage and still acts intermittent, then it’s the fan motor that’s shot. If the voltage isn’t constant, then you just track it upstream and find the break.

There’s no reason to suspect that the things inside the engine compartment (compressor, belts, etc) have anything wrong with them at this point. Everything you’ve posted points to a fan problem and that’s it.

You are correct that it wouldn’t work at all if the fuse was blown. It’s possible that the wire has come loose at the fuse box though.

Based on my limited experience as an idiot back yard mechanic, my money’s on the fan being the failing part.

Repair costs if you take it to a shop vary a lot depending on your vehicle. On some cars, the fan and resistor pack are easy to get to. On others, you just about have to disassemble the entire dash to get to the damned things.

ETA: I’ve never seen a clutch in a blower fan. They are usually just a simple electric motor with fan blades attached. Nice and simple, and you replace the entire thing as one part. The resistor pack is usually another separate part, but on some cars they are included in the switch assembly. The switch assembly may be just a small part, or you may have to replace a big expensive controller.

5

Sounds like the fan motor to me. Knowing what I do about BMWs, it might be a bitch to replace. Lots of dash removal and tight spaces.

Thankfully, none of mine have died. But if they do, I might have to go with “260 Air”.

EDIT: One of them is dead! Bought it that way, and never bothered to fix it! Another one has the A/C disconnected, but the heater works AWSOME!

6

I would bet on either a bad connection or a bad fan motor.
In my experience fan motor resistors either they work or they don’t. I have never seen an intermittent fan resistor.

7

I am driving a 2003 BMW 325xi. And I am somewhat handy, although I will admit to being somewhat limited with an automobile’s electrical system. I don’t have a multimeter, but I have no problem picking one up. Are they expensive or cheap, and are they easy to use, or do you have to know about electricity somewhat to use it properly?

I am fairly good at figuring things out if I can read how to do it in a manual, and it is pretty straight-forward. I have never really had any cause to screw with a car’s electrical system up until now, so I have been pretty lucky in that regard.

It was not doing anything different or funky at all. However, my wife drove the car last (for about a week), so God only knows what she did to it. A few things I noticed today when I started the car: the seat moved to a setting that would be much more suitable for her, which was a surprise to me (and my knees. It reminded me of that scene in Christine where the garage owner sat in Christine, only to have the seat move up to the steering wheel to crush the guy).

She has driven the car before, and she has adjusted the seat, and the seat memory never retained that setting until now… The radio was set to a station I never heard of before and didn’t even know existed. So all of those things were odd, but could be explained by her fumbling with the settings.

And one other thing… The temp. was set at 59 degrees, which my wife would have never put in. So, now that I am thinking about it, it is almost like something got reset, and perhaps those were the default settings. The radio station was the lowest possible setting on the FM dial. The temp setting was the lowest the car goes, and the seat was as close to the steering wheel that I ever have seen. Maybe that means something, or maybe it is just a coincidence. But if the car has an easter-egg kind of thing where if someone presses a combination of buttons in just a certain way and something bad will happen, I have no doubt that my wife would have found it. You can almost hear each car she gets into wince with fear when she gets behind the wheel. I’ve never known anyone as detrimental to the health to a vehicle as my wife.

She is to a car what kryptonite is to Superman.

Thanks for the advice. I will continue to seek out answers on the net and in this thread for another few days before I begin the process of trying to solve the problem.

8

Is it a manual system or automatic climate control?
In other words does it have a switch for the fan with desecrate fan speeds or does it something (button, whatever) that has an automatic setting?
If it has an automatic setting it does NOT have a fan resistor.
It will have a fan controller (sometimes called a power stage) that controls the fan sped steeplesly.

9

You can probably pick up a cheap DC meter for, well, cheap. But you might as well spend the money and get a regular multi-meter for general use rather then buying another one later when you need to test an outlet. If you don’t need to use it often, you can grab one from Home Depot for less then $40. Just make sure 12VDC is within it’s range for this project.

It does some like something went wonky with your car and if it has automatic climate control, the computer, I assume, can control your blower. For example, you can set it to, say 70, when you get in, nothing happens, when the engine warms up (in winter), the blower spins up, when the cabin reaches 70, it shuts down etc, like the furnace in your house, right…Based on that, and that you said everything else in the car had reset, I’d be worried that there’s something deeper going on.

However, I doubt the car’s computer controls all of those items (seat, radio, climate control). But, there may be something in common with them. That brings us back to bad wiring harness or ground in the dash somewhere.

Hell, start with the easy stuff, pop the hood and make sure no wires obviously are rusted out or chewed up by mice.

Start the car, put your hand under the dash, behind the radio, near the fuse panel, way up under the dash above your left food and just, gently wiggle some stuff around. Don’t try to unplug anything, but if anything is loose, you might notice your blower or radio turning on and off.

Long shots, sure, but they narrow things down pretty quickly, especially when the problem is intermittent.

The blower cutting in and out didn’t happen to coincide with hitting bumps did it? That’d be too easy.

10

I am assuming that I will be able to test these things with a multimeter? The loose ground I am guessing I would be able to eyeball. (I hope, anyway.)

The fan does not have the settings you describe inside the car, like most American cars. The fan doesn’t have a dial with an off/low/medium/high setting. What it has is two arrows, one pointing downward, one up. And it has (I think, anyway) 12 vertical light bars that grow from left to right as you push the fan’s up arrow (if the fan is at off, no bars will show.). Each speed gets 4 bars, and each push of the up or down button will add or subtract 2 bars at a time. So for instance, when the fan is off, all bars are dark. Push the button once, and the fan starts and two bars show. Push up again, and two more bars show. I don’t believe the fan’s speed changes, though. Pus ph it a 3rd time, however, six bars shoe and the fan moves to a medium speed. Next push is two more bars, but no change in fan speed. The next push puts the speed to high and adds two more bars. There is one more push that will illuminate the panel with all twelve bars, and that is the highest setting. But like I said, I believe it only has 3 speeds.

The behavior of the fan is very random. It will kick on for a few seconds and blow, but the speed is whatever it decides to be. And then it cuts on and off at variable times while driving, and when it cuts back on, sometimes the fan speed changes and sometimes it doesn’t. I didn’t do many proper tests, so I am probably failing at giving you a complete picture.

To me, if I were to describe it visually, it reminded me of a light bulb that has a loose wire or isn’t screwed into its socket completely. Sometimes, the light will flicker on and off, sometimes it will be bright for a minute before dimming. Sometimes when it dims, it will dim again and turn off, while other times it will go brighter, and flicker back and forth between medium and full brightness.

Just substitute “speed” for “brightness” and I believe you will get the picture.

I am not sure what “260 Air” means. But if it is in the dash, I am not looking forward to that adventure. I have never been inside this dash, and I never wanted to be inside this dash.

I would agree with this on the surface of what I’ve described. The way it is changing speeds with no discernible pattern gives me the impression thst zi hsve a loose wire somewhere.

11

Bolding mine. Problems with the blower motor, blower motor resistor, or a poor connection could cause it to cut out, but I don’t see how they could cause it to change speeds. I suspect a problem with an electronic component (control assembly, control module, or most likely output stage).

This system is complicated enough to be challenging even to a pro if he doesn’t specialize in BMW. I’m sorry to say I don’t think you’ll get very far with a multimeter.

12

Two windows down, sixty miles per hour. :slight_smile:

13

It has an auto button, but it also permits you to run it manually. If you get into the car and it is boiling hot, and start it while it is set to auto, the fan will go as fast as it can for as long as necessary until the desired temp is reached. It will then slow itself down. The defroster works like this, where when you hit the defroster button, it puts itself automatically into auto mode. When the car becomes to hot or cold, you can push on the down arrow once, and the system automatically goes into manual mode.

Based on what you wrote, my car should have a power stage on it.

I think I will try your “look for obvious stuff first” tomorrow. This is a good idea, and would have probably been my natural first step. However, it had nothing at all to do with a pothole or bump. This happened in my driveway.
Can I short out anything with a multimeter if I use it improperly? I would hate to make the problem worse by hooking something up incorrectly.

14

I know you are being helpful, but these are things that just don’t happen in a 2003 BMW.

A 71? Reach right up! An 88? Wow, that’s gonna take some disassembly! A 97? Wouldn’t even know where to start. A 2003? Seen em in the junkyard, and still couldn’t get shit out of the dash! Those fuckers are built!

Of course, this post is less helpful than yours, so maybe I should stop drinkin’ beer, shut my pie-hole and go to bed.

15

Saw this after my last post: No. And you can get a free multi-meter from Harbor Freight Tools with a coupon. Search for one online. But they don’t do continuity.

16

Actually, yes.
If you try to measure voltage with the meter set to Amps (especially on the 20A range), you will short out whatever you are touching with the probes.

17

I told you I should shut my pie-hole!

18

I think my current DMM might check for voltage when it checks for amps to prevent doing something like that. I’ll always miss that shower of 120v sparks that scares the bejesus out of me.

Set the DMM to DC and, if you need to, make sure the leads are in the right place (with the V between them). They all work a little differently, read the directions before you go sticking them in an outlet, and about the only way you can short something is to have one lead touch two wires.

19

A quick search found this http://www.bimmerfest.com/

I suggest you join up and do a search, there seems to be plenty of others with similar problems.

20

A likely reason for an intermittent electric motor is worn out brushes…
They are carbon rods that touch on the communator… Its likely you can get the brushes replaced.