possible alternator failure
 

hey guys,

i recently bought a 320I 1992 bmw (automatic transm.). I had some problems with the A/C, so i ended up changing the compressor and fixing the evaporator. the A/C is great now, but i've noticed that when i do the kickdown, the A/C gives relatively hot air but the engine is running fine. I though it might be the alternator, or the battery. The mechanics said that the alternator needs to be replaced. The reason i'm posting this is that i don't trust this mechanics at all, maybe u can help me troubleshoot....


thanks in advance,
enjoy ur bimmers :D

John

That is normal operation. Our cars (standard and automatic) are equipped with an A/C cutout device that shuts off the compressor under moderate to hard acceleration, to eliminate the power draw of the compressor. It cuts back in while cruising. The alternator will not cause this problem. To check it, simply put a voltmeter across the battery terminals while the car is running, voltage should be approximately 14.0 volts.

thx for the tip kingnine, I will buy a voltmeter and start investigating myself. I feel that the electricity in the car is low. whenever i put the headlights on, the radio led goes dimmer. if the voltmeter gave me 14, so it must be the battery then. I'll post back as soon as i know something new.

laters,
John

hey again,

I have measured the voltage, its 13.5/.6 at the battery with the engine running. is that in the acceptable range?

thx,
John

Yes, that is acceptable. If it drops below 12.6V, the battery is discharging. (What does it read with the engine running and the headlights on?)

If it goes over ~14.5V, the battery is being overcharged.

--DD

I have measured the voltage at the battery while running the engine having the headlights + A/C on and it was around 13.2 or somethin.

regards,
John

Wait a 'sec, if you turn on the headlights, shouldn't the radio lights dim?
That prevents them from being too bright at night.

It definately does that on my other (non bmw) cars. I have not noticed on my BMW though. Will check that out, but I think I'm right.

David S

It's also not a bad idea to turn off the A/C compressor if you plan on accelerating quickly. Takes some of the strain off the engine.

well, it seems that its quite normal for the lights to go dimmer to match the other lights(stereo, A/C buttons....) well, i'm paranoid a bit, i just bought the car :D. It seems that it does cut off the A/C automatically when I give it a kickdown. Turning off the A/C is not an option here, specially having +50C !!! I am worried about a small piece of plastic(+sponge) that was thrown out of the A/C output terminal just a while ago, it was making some weird sounds when I put the fan on 4. This piece was making the sound, but i don't know where it did come from, its an internal part though. I will try to check the A/C filter because there is no way that this piece can make it through the filter unless its torn.... trying to repair the car on my own is pretty difficult here, as i mentioned, +50C is simply non human :o .

thx guys,
John

That is correct, when you turn on the headlights, the radio lights should dim.

John,

It might be an easier task to rule out a battery problem for now. Most of the local parts chains will load test a battery for free.

You could still have a bad alternator, but at least you'll know if the battery is contributing to the problem or not.

Rich F

have you checked your battery connections? ive had situations like this where simply cleaning the terminals solved the problem.

my alternator and battery are in a good condition. it was just another mechanic trying to make money out of nothing. thx for all that replied.

I was checking http://www.logun.org when i found out that the head-light switch is illuminated, i changed the small bulb and its all working fine now. does anybody know if the window buttons illuminate? i mean the buttons next to the transm. ??

thx,
John