Turn the car on, turn on the defroster, make sure the inside temperature control is set above 70 degrees, relax. The car will automatically turn on the PTC electric heater elements until the car thinks the engine waste heat will do the job. If you have a lot of frost then adjust the inside temperature control to max heat, the engine will probably keep running to try to produce the heat demanded. And if you are having a lot of frost problems you should install an engine block heater and block up your front grill.

Wayne