Differential air pressure type switches are utilized to monitor the
correct operation of each of the blower motors employed.
Correct rotation of the motors is necessary for the switches to
properly operate. These devices use a diaphragm to sense
pressure and to mechanically trigger a SPDT Snap Switch
when the proper pressure is developed across the blower
wheel. If a loss of pressure / airflow were detected, the switch would
open causing power to be removed from the heaters. Loss of
airflow may result from a motor malfunction, reversed motor
rotation, a loose blower wheel, or reversed air sensor tubes.