I have residential Janitrol electric heat pump that is approximately 13 years old. The air handler fan has stopped working around noon for the past four saturdays, allowing the inside coil to freeze over. Last week it also stopped on Tuesday.I can rotate the thermostat from cool,to heat,to emerg heat, to cool again and the fan will start and cycle like it should for another week. What is going on?

Bad fan relay is my 1st guess (could be on a PC board). Thermal overload on motor would be my second.
But wait there is more. Thermostat might have dirty contact not sending 24 volts to the air handler green stat wire, the unit was actually supposed to turn off and the condenser contactor welded closed and froze the coil. All I can think of right now.:)

If you leave the heat and cool switch OFF and put the fan switch to the ON position, will the blower stay on or will it go off after a while. If it stays on and doesn't go off, you probably have contactor problems. If it does go off, you probably have a bad fan motor that's over heating and going off on thermal overload.