is there a light on the magsafe charger?
before exchanging it, do one thing first:
- Shut down the computer.
- Plug in the MagSafe power adapter to a power source, connecting it to the Mac if its not already connected.
- On the built-in keyboard, press the (left side) Shift-Control-Option keys and the power button at the same time.
- Release all the keys and the power button at the same time.
- Press the power button to turn on the computer.
Note: The LED on the MagSafe power adapter may change states or temporarily turn off when you reset the SMC.
On a new macbook Air, there is no need to fuss with it, return it for another Air in exchange.
Messing with it / diagnostics at this point are fruitless when you can exchange it, especially on a power issue.