Mach 15's? Ours isn't ducted and does NOT have a Wall thermostat. MUST be run with Fan on HIGH or it will freeze up. You should probably do the same. That said, if yours have wall thermostats, they should be stopping the compressor to prevent what just happened.
Have you ever cleaned them? If the Condenser coils are dirty, the reduced air flow there will promote freezing of some of the condensate water. Then the ice pack can spread across the coil and cause a full freeze over.
Remove the plastic shrouds, then the sheet metal covering the top of the "indoor" coil (properly called Evaporator) on the front end of the A/C units. Clean that coil and the drain pan with the drain holes at the two ends (left and right). Make sure Freeze Sensor is clipped to the Coil.