everytime i turn the ac on the voltage drops a lot and car almost dies.
i replaced the alternator and still the same thing.

need some help let me know

 

ummmmm....I think you should look at it the opposite way, the reason the voltage drops is because your idle is dropping, idle drops then the alternator spins slower, hence lower output. Check your idle control solonoid, etc. when you turn the A/C on, the idle should remain the same. Keep in mind that the battery should hold at least 12.5 volts when loaded too.

 

How about the possibility your A/C compressor is locking up???? .....

 

Could an overly tensioned belt cause this?

 

i would check what thunderjet429 said the ac compressor, if it is locked it can cause all types of problems. take the belt off and see if you can move the pulley by hand

 

You will be able to turn the pulley by hand, UNTIL the clutch engages.... unless the hub is going out but i doubt that it is since it isnt having a problem until the A/C is turned on.

 

true, but if its locking up bad enough to stall the car then engaged you should be able to feel play. you could take the belt off and run the car and turn on the ac and see if the problem still persists to try and rule out the ac clutch but im guessing the clutch is shot. also with the belt off and car running try and turn on the ac and see if you can hear noise coming from the compressor, then try and work the pulley by hand

 

id check the belt then your iac. your idle air control helps your car keep its idle under excessive load. especially the a/c. you could have a bad gasket behind it, or if its the problem it could just need cleaned out which carb cleaner has always done me good. anyway good luck, if it is the clutch on the a/c bypass it, youll like it more.