sorry for the long post, but i believe information=knowledge=power :)
this is interesting... my friends car was/is having similar problems, here's the situation:
we live in New Mexico so it gets pretty warm in the summer, and now that summer has hit us, this problem has popped up. it all started when the ignition interlock failed (bad choices, my fault, i failed as a friend, anyways...) that seemed to short something out and the battery got completely drained. a jumpstart the first day worked fine, but the next day at work, a jump didn't do anything and the interlock was having problems. so, we towed it to get the interlock reinstalled/serviced... done. the next day, she was at a stop light with the ac running, and the car felt like it was about to die (power drain?). the radio's volume would fade in and out and the car was on the verge of stalling. the car was taken to autozone and had the alternator checked. both the alternator and drive belt were found to be bad(i guess the alternator was tested "in car"), so both were replaced on the spot. however, after they were replaced the problem continued. that is to say that, while idle, with the ac on, the car seemed to be on the verge of dieing. this perplexed the autozone guys, so they tested the alternator a second time "out of car"... this time the alternator came back fine. my friend doesn't take any crap from anyone, she's an amazing girl! so she spoke to the manager, and because of the situation, got a new battery, the original alternator put back in, and was only out the cost of the belt. the next day, same thing... stopped at a light, ac on, radio in and out, seemed to be on the verge of stalling. so she had a different mechanic look at it while at work and he concluded that the alternator was bad (again). so i decided to just replace the damn thing myself... done. now, i can understand that even though the battery was replaced, if the alternator is bad it's not going to recharge the battery. this was the case for a couple days before i actually replaced the alternator. so once i got the new alternator installed we fired up the car and everything seemed fine. we turned on the ac full blast and i felt first hand what was going on... the car was idle (just under 1000rpms) but once the ac was turned on it would drop down to 300/400rpms? up, down, up, down, up, down ect... i thought that if the previous alternator was bad then the battery may have been drained even though it was new (as the car had been driving two days before i put in the new alternator) so i sat there for a few minutes idling the car a little bit higher to recharge the battery... within a few minutes this seemed to fix everything! radio on, full blast, no problem, ac on, full blast, no problem. two days! no problem! but now, the check engine light has come on!? so this is the point where im not sure what to do...
so i can verify that;
1. the negative cable to battery is in clean condition
2. the s-belt has been replace and is within measure (this is the one belt in front right?)
3. new alternator
4. new battery
but how can i trouble shoot;
5. AC compressor / clutch
6. catalytic convertor or air/fuel chain clogged
im also looking into seeing how much it would be to have a tech/mechanic read the error codes that should be generated from the check engine light.
i know i need to top off the oil, she is running a little low, and will be doing a full oil change for her come july. i know i can do that. im also gunna find out how to check spark plugs (never had to do that, so i'll be researching that now) so lets assume those will be fine... i'll repost if thats not the case and fixes the problem.
THANKS IN ADVANCE!!!
These board have already been such a wealth of information!!! everyone here is super badass in my book!