It sounds like a relay has stuck shut. It would not be wise for you to go poking around in the control box if you don't know what you are doing, you could turn the A/C off at the fuse panel which I'd recommend doing and then call the repair service. Once the relay sticks it needs to be replaced there is no repair for it.

Air flow to the evaporator may have been reduced and frost built up in the coils. That can be caused by a dirty filter or an obstruction in the vent. The controller is getting odd signals as a result and the whole system isn't operating as it should. Turn off the power to the unit, allow the frost to melt, fix obstruction to the air flow (replace filter, unblock vent, etc), and then it will work!