Intermittent heat problem with Rheem electric furnace


I'm having an intermittent problem with my 7 year old Rheem electric (forced air) furnace. About 2-3 random times a week the furnace will fail to turn on despite the room temperature being below the thermostat set value. To get it to function normally, I turn the furnace off (at the thermostat), wait a few seconds, and turn it back on. The furnace will then return to normal function from anywhere from 12 to 72 hours, then it'll happen again.
Other interesting notes. When the furnace is 'malfunctioning' I have seen the heating coils on, but not the fan (this obviously should never happen). My immediate thought was that the blower motor was going bad. The problem with this theory is that the blower always comes on when I turn the fan on at the thermostat. So it appears to me that the thermostat is either not sending the command to turn the blower on (but is telling it to turn the heating elements) or that the furnace is unable to always get the motor going. The thermostat is digital (White-Rodgers) so it seems unlikely that it would work intermittently.
Oh and I did replace the motor start capacitor because it was cheap and easy. It didn't help.
I am stumped. Anyone have a clue here?
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I don't know anything about this type of furnace, but I'd like to take a stab at what it may be. I would think it normal for the heating elements to come on without the blower. I would think there would be a sensor in the heating chamber that turns on the fan at a set temperature, and off at another set temperature. I would believe this or another sensor would also turn off the elements if the blower didn't come on and the heating chamber reached a set high limit. Because this is an electric furnace, this sensor would have to be acting through a contactor for at least the heat part, possibly the blower as well. If there is something wrong with this sensor, it may be causing the safety control to go into a lockout mode

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