Stopped working smells like something burned?

If this is a ducted unit with a wall mount thermostat, remove the inside cover from the AC unit. There is a silver box with the electronics inside. Remove this box and remove the cover. Visually inspect the connections where the 120VAC connects. If that looks ok, then check the relays on the printed circuit board. If these look burnt, replace the control box. If they look ok, check to see if there is power coming in to the unit. If not, check the breakers and make sure they are ok.

Thanks,

Jeff