A Thermal fuse doesn’t blow for lack of airflow, the thermal cut-off on the heater duct does that. Thermal fuses blow for 3 reasons, old, element grounded to chassis and a bad hi limit stat not opening till the op stat or thermistor on blower house takes presidencce. To test airflow use a temp probe on meter and angle inside door floating mid drum. When heat goes off after 200 degrees should see a 1-2 degree drop per second minimum for efficiency.