L.B. White AD100 Owner's Manual page 14

AIR PROVING SWITCH
The air proving switch is located on the fan housing at
the motor end of the brood heater. It must work properly
to allow an ignition cycle. If the air proving switch
contacts are closed before the igntion control starts the
fan motor, or do not close on a call for heat after the fan
motor starts, ignition will not occur . See Fig. 9a or 9b.
AW060/AW100/AW250 service (Fig. 9a):
-- Remove the two (2) sheet metal screws holding
the switch with bracket to blower housing.
-- Remove the assembly by turning the switch so the
paddle on the switch arm can be pulled through
the oblong hole on side of fan housing.
AW325 service (Fig. 9b):
-- Remove the two mounting nuts and slide the
switch from its mounting screws.
FLAPPER (SAIL)
The flapper, located within the housing at the blower
discharge, works in conjunction with the air proving
switch in proving that proper air flow has been achieved
by the fan and motor before allowing an ignition cycle to
continue.
If the flapper is binding, its arm will not engage the air
proving switch and ignition will not occur.
Ensure the flapper lifts freely, that it does not bind on the
fan housing and that it is free of dust and other debris.
14
FIG. 9a
AIR PROVING SWITCH
Fig. 9b
REMOVE COVER
(AD325 ONLY)
REMOVE
NUTS
FIG. 10