Ok, I have gone through 3 alternators with my car!

Normally the reading is about an 1/8" above the middle line. That's fine as far as I've found.

I just had my A/C fixed, and now every now and then (with the A/C on) it goes negative. Not all the time, and usually just under 1500rpm.

I do have a stereo with an amplifier in my car, but it's only 1000w, and I don't always use it.

I can have the system bumping at ear-bleeding volume and not have the needle move.

Sometimes I can have the wipers, lights, stereo, and fog lights all on and have no problems, the gauge will be +.

Sometimes I can have NOTHING on, and it goes negative! This, once again, is at idle to about 1500rpm.

All my connections are tight. I have all my grounds. The alternator is a stock replacement 110 amp.


What is wrong!!!???

 

I have experienced a similar situation recently where my voltage would drop while at idle with the A/C on. After doing some checking, I found that these voltage drops coincided with the clutch on the A/C compressor engaging. I can't say that the same thing is happening to you, although it could be. BTW, I also found during this checking that the freon charge on my car was almost non-existant. Oh well, I had been planning to do the R134A conversion anyway.

 

Hmm, that would make sence when the A/C was off, but this happens when it's on too!

I just (Friday) had my A/C converted. Well, I should say replaced, as I needed a new condenser and all the lines!

 

It is happening to me when the A/C is running, that is how I noticed the problem. Once I get it converted and fully servicable again, I will continue my search for the actual problem.

 

Had this with my car. Started as you describe, got worse until the headlights would go dim/bright all the time. Long story short. loose screw inside the alternator that grounds the diode pack to case. Guess it would heat up and fail, cool and reconnect. Could wiggle the plug in connector on the back of the alt and it would work fine for a minute or so.

 

Hmm, I'll check that out, but like I said, this is my 3rd alternator! It's not just that this problem keeps happening, but that my car eats alternators! I've only had the car 2 years!

Also, I don't know if this is related or not, but when I put the car into neutral (to coast or come to a stop), the car bogs down to around 3-400rpm, sometimes stalling. The lights pretty much go out at that point... but that's probably because the pulley isn't spinning enough. Would putting a drain on the alternator when it's not putting enough out smoke it?

 

Did you ever find the cause of the problem?