I've been searching for the past 30 minutes (have read through about 30 pages of threads) and can't seem to find the same issue I'm experiencing. Here's the details:

Car: IX, bought brand new in April 2007
Mileage: 39XX
Voltage (before this weekend): usually 13.8-14.0volts
w/AC on at idle (before this weekend): usually 13.8-14.0volts and drops to 13.6 when AC compressor kicks on when at idle
Engine RPMs (before this weekend): at idle, always stays at 800 after car is warmed up...regardless if AC is on or off

I had a DEI Hornet car alarm installed this weekend. And after that, here's what's happening:

Voltage (no AC): NO CHANGE FROM BEFORE...stays consistent at 13.8-14.0volts at idle or when driving
Voltage (with AC on): with AC on it dips nearly to 12.0volts when at idle
Engine RPMs (no AC): NO CHANGE FROM BEFORE...at idle, stays at 800 after car is warmed up
Engine RPMs (with AC on): dips down to about 500rpms...car doesn't stall but sure feels like it could


Having the alarm installed is the only thing that changed over the weekend. I can't imagine that the alarm would have this type of effect on voltage and engine RPMs. Could it?

 

Yes, alarm did it.

 

It could be a good chance the alarm is causing you all the problems.My dad had an alarm installed with a engine start kill on his car and because the wiring was done incorrectly, his car would not start all the time.Turned out all of the power was being sucked out of the battery because of the bad wiring.Once the alarm was taken out, the car started every single time since than.

 

Thanks for he replies. I figured it had to be the alarm, but just couldn't figure out why an alarm would have this issue only when the AC is on. Car starts fine. Oh well. Back to where I got it installed so it can get fixed.

 

Have your problem been fixed already? Because I have same problem too!