Car Trouble: Air Conditioner + Headlights = Bad

Factual Questions
1

1998 Saturn SL with around 89,000 miles.

When I have the headlights AND the air conditioner on, the car’s performance suffers. It will sputter, bog down, and briefly (like, less than a second of duration) stop and then come back on again. This problem only happens with the A/C AND the headlights on. With headlights on but no A/C, no problem. Ditto for having the A/C on but no headlights.

Best I can figure is that there is an issue with my alternator, but that’s little more than a WAG.

Some background information that may or may not be relevant:

  1. About two weeks ago I had the serpentine belt replaced at the local dealer from where I bought my ride. A spring holding the tensioner in place had come loose, so they fixed it and replaced the belt.

  2. Wednesday of this week we had pretty severe flash flooding around here, and at one point my car was in water pretty deep - like up to the bottom of the oil pan, if not deeper. I managed to somehow drive it out, but I wouldn’t be surprised if I got something wet that I shouldn’t have.

Any help here?

2

I’d have them adjust the “idle” on your car but have them do it with the headlights, a/c, radio, and wipers on.

3

On a '98, the “idle” is going to be computer-controlled.

4

The alternator may be weak. It’s pretty straightforward to test for that.

There may be a poor electrical connection related to a battery cable or a ground wire somewhere. A competent mechanic can test for that.

5

Sounds exactly like a slipping serpentine belt. The more load the alternator is under, the more torque required to turn the pulley.

I would take it back to the dealer who changed the tensioner and report exactly what you just stated.

IANAM