the most obvious sign would be that the light on the dash would be on. but if you start the car and put a voltmeter on the battery terminals it should read between 14v and 14.5v
If your talking about cars... If you smell a burning smell, or your red battery light comes on then i would get your alternator checked out!
A warning light on the dash would illuminate.
Turn car on remove positive battery terminal if car turns off alternator is bad
When your battery does not get charge.
Typically you know your alternator is out when you have to jump start your car numerous times. A way you can test it is by turning on your car and while it's running discount the + terminal. If the car turns off then your alternator is bad. If the car remains in then alternator is good and possible bad battery. Hope this helps
If it is makeing a noise or is not putting out at least 13.5 volts it is bad. Take the car or the alternator to an Auto Parts store and have them load test the alternator to be sure.
You would probably toast the diodes in the alternator.
A bad alternator will cause a battery to go bad. It does not have an effect on the air conditioner.
A bad belt, a bad regulator in the alternator or bad brushes in the alternator.
with vehicle running pull posative side battery terminal off if it quits alternator is bad
To test the alternator if funds are low, let the motor idle and remove the negative battery cable, if the motor dies its probably the alternator.
Check voltage with a voltmeter at the battery With engine running readings should be 13.8-14.2 With engine running hold a screw driver to the back of the alternator, if there is no magnetic field, the alternator is bad.