Flapper Adjustment; Testing The Manual Reset High Limit Switch - L.B. White AD250 Owner's Manual And Instructions

1. Shut off the gas supply to the heater.
2. Disconnect the heater from its electrical supply.
3. Make sure there is not any dust, dirt, etc. that may
cause binding on the pivot points of the flapper as it
rides within the blower housing. If debris is found, use
a soft brush, or compressed air, to clean the area as
necessary.
4. The arm of the flapper should engage the arm of the
airflow switch when the trailing edge of the flapper
body is lifted and is approximately 31.7 mm to 34.9
mm off the blower housing bottom. At this distance
you will hear a click which are the contacts closing
within the switch mechanism.
5. If the switch contacts do not close within this distance,
then manually push in the arm in the switch to make
sure the switch is not defective. If a click is heard, the
switch is good and the flapper arm then needs to be
adjusted to engage the switch arm.
Fire H H azard
■
Do not operate the heater with the high limit switch
bypassed.
■
Operating the heater a bypass high limit switch may
lead to overheating, possibly resulting in a fire, with
subsequent damage to the heater, building damage, or
loss of livestock.
The high limit switches should be tested a minimum of once
per year when the heater is given a thorough cleaning.
1. Disconnect the heater from its electrical supply.
2. Remove the high limit switch.
3. Holding the switch by one of its mounting legs, apply a
small flame only to the sensing portion on the back of
the switch. Be c c areful n n ot t t o m m elt t t he p p lastic h h ousing
of t t he s s witch w w hen c c onducting t t his t t est.
4. Within a minute, you should hear a pop coming from
the switch, which indicates the contacts of the switch
have opened. Check for lack of electrical continuity
across the switch terminals to verify contacts have
opened.

TESTING THE MANUAL RESET HIGH LIMIT SWITCH

WARNING

FLAPPER ADJUSTMENT

6. Using a needle nose pliers, gently bend up the arm of
the flapper (NOT T T HE S S WITCH A A RM) in increments
until the flapper arm engages the switch arm, closing
the contacts of the switch when the flapper body
trailing edge is 31.7 mm to 34.9 mm of housing
bottom.
FIG. 13
BLOWER OUTLET
OF HEATER
AIR PROVING
SWITCH
ARM OF
FLAPPER
AIR PROVING
SWITCH ARM
5. Allow the switch cool down for about a minute before
firmly pressing the reset button on the switch.
6. Check for electrical continuity across the switch
terminals to make sure the contacts have closed.
7. Reinstall the switch back into the heater. Reconnect
the heater to its electrical supply. Start the heater and
check for proper operation.
FIG. 14
RESET BUTTON
TERMINAL
MOUNTING
LEG
FAN WHEEL
PIVOT POINT
OF FLAPPER
PIVOT POINT
EDGE OF
OF FLAPPER
FLAPPER
FLAPPER
31.7 MM TO 34.9 MM
SENSING
SURFACE
FLAME
16