L.B. White AD100 - Manual (Page 16)

15
MANUAL RESET HIGH LIMIT SWITCH
WARNING
Fire Hazard
■
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.
This heater uses a high limit heat switch for the purpose of
over heat protection. The high limit switch is located on the
heat chamber, and is wired in series between the ignition
control and the gas control valve. See Fig.15 (AD100) or Fig.16
(AD060).
The switch has normally closed contacts. If an overheat
condition occurs, the switch contacts will open, thereby
opening the circuit to the gas control valve.
The high limit switch should be tested a minimum of once per
year when the heater is given a thorough cleaning.
FIG. 15
FIG. 16
1. Holding the switch by one of its mounting legs, apply a
small flame only to the sensing portion on the back of
the switch. See Fig.17. Be careful not to melt the
plastic housing of the switch when conducting this
test.
2. Within a minute, you should hear a “snap” 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.
3. Allow the switch cool down for about a minute before
firmly pressing the reset button on the switch.
4. Check for electrical continuity across the switch
terminals to make sure the contacts have closed.
5. Reinstall the switch back into the heater. Reconnect
the heater to its electrical supply. Start the heater and
check for proper operation.
FIG. 17
AIR PROVING SWITCH WITH PADDLE
The air proving switch must work properly to allow an
ignition cycle. If the air proving switch contacts do
not close on a call for heat after the fan motor starts,
neither spark nor ignition will occur.
1. Remove the two (2) sheet metal screws holding
the switch with bracket to blower housing. See
Fig.14.
2. Remove the assembly by turning the switch
assembly so the paddle on the switch arm can be
pulled through the oblong hole on side of fan
housing.
3. Disconnect the leads from the air proving switch.
FIG. 14
RESET BUTTON
SENSING
SURFACE
TERMINAL
FLAME
MOUNTING
LEG
HIGH LIMIT
HIGH LIMIT