The issue may lie with the Thermodisc. Follow these steps to diagnose the problem:

1. Turn off the blower switch.

2. Disconnect the wires from the Thermodisc.

3. Bypass the Thermodisc by connecting the wires from the swtch & fan together.

4. 
   

If the fan or blower activates after bypassing the Thermodisc, this indicates that the Thermodisc is faulty and needs to be replaced.