I was wondering how can test my alternator? My 05 GXP drops voltage every time my HVAC system is turned on. Instead of it being slightly over 14v it drops about half way between 14v and 9v when HAVC is on (stereo and all the rest are completely turned off and interior lights dim a bit when they are on), second it’* turned off the voltage jumps back up.

I tried starting the car and disconnecting the battery with HVAC off, the moment I disconnected the battery it dropped down a little bit then back up to normal and the car stays on.

Also my battery isn’t charging right. I can leave my headlights on for less then 5 minutes then my car won’t start. I took my battery to Napa they tested it and showed “very good” on the testing unit. Could it be possible that the alternator not charging it right? Or could it be a bad battery?

any input is appreciated

thanks
Samz

Check this out [YT]http://www.youtube.com/watch?v=dq24oPUVmdA[/YT]

Let me know how this turns out for you. This is definitely information that would benefit other Bonne GXP owners.

I just tried that, I guess my alternator is fine.
something else is wrong

Here’* how it went
Before starting it read 12
While starting it read 10.5
After starting 14.5 with HVAC off
After starting 11.5 with HVAC on

could it be the battery? because it dies very quickly when i leave my lights on stereo on

do you have the same problem?

does your voltage drop when Hvac is on? see im not sure if this is normal or just my car.

My voltage drops for a number of reasons. I have heard that GM cheaped out on the wiring and used wiring that'* much too small. I will be running some extra wiring inside my car to see if that helps alleviate the problem with the voltage dropping so often.

However, I am able to start my car without any problems. I have an optima battery, but I doubt that makes a difference in this case.

I'm going to say its your battery. Even if you had it tested, it won't come back as completely failed if it holds any measure of a charge.

the huge drop from HVAC would lead me to believe your alt and/or battery are going south, or the HVAC system itself is drawing far too much current...

but since leaving the lights on for 5 minutes or less causes the issue, HVAC is taken out of the picture... and since the alt will raise terminal voltage to 14.5, i have a hard time believing it'* the alt.

Have the battery load tested. You might have a cell going bad in the battery.

thanks rob, and kevin ill give that a try tomorrow before i buy a new battery

can you let me know if yours drop when you use the havc?

Can't you take the altenator out and have it checked at Auto Zone, or you could have the charging system tested while the car is running at Auto Zone.