I have a Rheem electric central heating system that when in the heat mode will not turn on the blower when the thermostat is in the auto position. The heat coils will come on but the blower will not come on unless I put the fan switch on the thermostat in manual position. I am trying to determine if the problem is with the thermostat or in the relay inside the heater compartment that turns on the blower. Any assistance will be greatly appreciated.