Depends what your switchover temp is set at. If it is 35 or below I would recommend thawing it(just through the top-grill, don't remove any panels),with some luke-warm water to ensure that the fan blades aren't frozen and all system components are free.
Just make sure you kill power to the unit before you do this. If your system hasn't been serviced within the last couple of years, that would be a good time to call a pro and have it done to ensure your system is running at peak efficiency.