I have an old ruud cental air unit and when the thermostat calls for heat, the heat comes on but the blower does not turn on. Is this the fan or is it possibly the controls which turn on the fan. It is an old unit. It is a natural gas unit and it has an electronic Ritetemp thermostat . It will not turn off if you try to turn it off at the thermostat and inorder to turn the unit off , you have to go to the attic and unplug the 120 volts going to the unit. Could the problem be in one of the controls such as the transformer or other switches . The unit is probably around 15 to 20 years old .

Bad fan/limit control or motor most likely