KeithO

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.

KeithO

Just got back from a test drive/auto parts store visit. I removed both the fuse and the relay prior to going anywhere (previously, I just had the fuse removed to allow the battery to charge).

Everything seems normal. I bought a replacement relay for about $15.

However, I have decided that the best way to ensure that the battery won't drain in the future and to esnure that I actually addressed the problem is to do the following:

1) Leave the fuse and relay out of the car overnight.
2) See if the battery is alive tomorrow morning before I leave for work. If it is, leave it as-is for about a week and make sure. If not, start the fuse pulling game again.
3) If the battery is no longer draining overnight after about a week, re-install the relay and fuse and watch it for another week. If no problems, then it is fixed. If problems then more troubleshooting is required.

I don't think my wife will miss the AC this week. It will rarely be above freezing this week.

I'll report back - it just might help someone else.

jplinville

If she uses the defrost, she'll miss the AC, as the system energizes and cycles during use.

73shark

Only if the ambient temp is above 41*F.

KeithO: Can't you check the current draw w/ the new relay and the fuse in to see if that fixed the problem?

KeithO

Lack of AC doesn't both me, even for defrosting... I've had a long, bad, storied history with GM AC systems and after a car gets old enough, I let them die and don't fix them. Besides, I also know that newer cars won't let them run below a given outside temp because it ruins them - 41 deg. would make some sense.

I suppose I could check the current draw but I got lazy. I only worked one day between Dec 23 and today but my "honey-do" list grew all year and this break was supposed to address this . My plan was to have a day or two of relaxation but my "projects" ate more days than budgeted and then this stupid battery drain thing came up. Once I got to the state above, I decided to plop myself on the couch and do nothing for the rest of yesterday.

I suppose any follow up can happen during the evenings this week, should I get the motivation.

73shark

The reason the compressor doesn't turn on below 41*F is to prevent the evaporator from freezing up. Same reason the system won't cool the air below about 40*F in the summer. It doesn't ruin the system, it just won't pass much air when the evap is a chunk of ice.

KeithO

Battery drain problem is gone.

I left the AC relay and fuse out of the car for about 5 days without problems. I reinstalled the relay and fuse 5 days ago and still no battery drain.

I guess this problem is solved.

KeithO

Now that it is warm out - this is back.

The AC stopped working yesterday. The no-name autoparts store AC relay was clicking and when I fiddled it, it clicked even more. I had my wife go to the Chevy dealer to get a new Delco one. I just installed it and went around the block - viola! AC works. However, the new relay emits a buzzing sound. I turned off the car and removed it and it was smokin' hot.

My theory is that something else is wrong with the AC system which caused the original AC compressor relay to failed closed, engaging the compressor clutch and draining the battery. The no-name one just failed open, which is why I had no AC but wasn't draining the battery. I didn't beat the new one enough to make it fail but clearly something is wrong.

Anyone have any idea what I should be checking?

KeithO

I got to the bottom of this. A family of mice set up a home under the underhood fuse block. I guess they couldn't resist chewing on some wires while they were in there.

73shark

Glad you found it. Lucky that five amp draw didn't heat something up enuf to start a fire.