What exactly are you asking? Do you mean that the compessor is not working or stopped moving, and why that the engine is still running? I am confused.......
The outside of the evaporator froze up. The evaporator is the part in the HVAC plenum under your dash. If you were to see it, it would look like a small radiator. Warm air from the outside passes through the evaporator which is chilled from the refridgerant (probably R-134A) running from your AC compressor. If you keep the AC on long enough, humidity from the outside air will start freezing to the outside of the evaporator. Eventually enough humidity could freeze and block the flow of air through the evaporator. The ice is of course on the outside of the AC system, so the refridgerant can still flow. since the refriderant is still flowing normally, Your AC compressor continues to function normally I assume the motor you mention is your AC compressor If you mean your blower motor, then the AC freezing would have no effect on the blower motor because cars arent wired that way. Not only does your car have no idea that your AC is frozen, but it would have no way of telling the blower motor to turn off because of that.
the electric motor; Temperature switch
I am assuming you are asking about a residential AC unit, since Ruud doesn't make mobile ac units. I would check the refrigerant level in the unit, If the refrigerant level is low, this can cause the evaporator to freeze up (ice over), along with the line to the compressor. Also check the evaporator core for dirt or debris blocking the air flow through it. you will need a licensed technician to add refrigerant, since the unit probably uses R-22.
