Diagnose things first. What does the ice look like? If it is white and frosty looking it is an airflow problem. If it is a hard clear ice then it is either a drain problem or possibly low refrigerant charge. However, yours is a bit different so I would suggest that you shut your A/C off, turn off the breaker, and try disconnecting the thermostat (temperature control knob). Make sure the wire(s) are not touching anything and turn the breaker back on. Does the A/C run? If not then the thermostat is the problem, but if it does run then you need to find a relay or contactor that is stuck shut. This it where the wiring diagram comes in handy.
Tom