Over the last few weeks, our 'burb's battery has been dying when left to sit overnight. Among the new parts that I threw at the car were a new battery and a new alternator. No dice - it just took a little longer for the car to be completely dead with the new battery.
This morning, I took the alternator to the auto parts store just to confirm that it was OK - it tested OK.
I then came home and reinstalled it.
From there, I disconnected the positive battery cable from the battery and jury-rigged my multimeter to be in series with the battery cable, completing the circuit (One probe on the positive battery post and the other on the cable).
This is what I saw:
With the car off, something was pulling an average of 5 amps - that is alot.
I did notice a clicking sound low, on the passenger side of the motor as I connected up the circuit. It made me wonder if it was the starter but maybe it is something else...
I sequentially started pulling fuses, watching for a meaningful change in current draw. When I pulled the 10amp fuse labeled "AC COMP", the current started dropping and after a few seconds settled on zero.
To confirm, I started playing with putting it in and out to establish a pattern, but it appears that I killed the battery along the way.
I have a battery charger with an ammeter. Normally, it starts a charge at around 8-10 amps and tapers down over a period of hours to zero amps. At zero, I know the battery is fully charged. Since I started having this problem, the battery wouldn't charge and the ammeter seemed to settle on about 6 amps (just like above).
Right now, I have the AC COMP fuse out and the charger on the battery. It appears to be charging normally and as of a few minutes ago, it had gone steadily from 6 amps to 4 amps. Once it starts to converge towards zero, I plan to re-insert the fuse to see if the ammeter jumps up again.
My current theory is that the AC Compressor relay has failed and failed energizing the AC compressor.
I should be able to prove this theory by the end of the day. I will report back what I learn.