Air Proving Switch; Manual Reset High Limit Switch; Gas Control Valve - L.B. White Therma Grow 120NG Owner's Manual And Instructions

AIR PROVING SWITCH

1. Remove two sheet metal screws holding air proving
switch assembly to blower housing. Remove
assembly by turning switch assembly 90 degrees so
the switch paddle can be pulled through oblong hole
on side of fan housing. See Fig. 12.
3. Disconnect the leads from the air proving switch.
4. When installing replacement switch, use care in not
bending the switch arm, otherwise ignition problems
may occur. Replacement includes mounting bracket.
TESTING THE MANUAL RESET HIGH LIMIT SWITCH
n
Do not operate the heater with the high limit switch
bypassed.
n
Operating the heater with a bypassed 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 switch should be tested a minimum of once
per year when the heater is given a thorough cleaning.
1. Remove the high limit switch from the heat
chamber.
2. Holding the switch by one of its mounting legs or
electrical terminals, apply a small flame only to the
sensing surface on the back of the switch. Be
careful not to melt the plastic housing of the switch
when conducting this test.

GAS CONTROL VALVE

1. Remove the following
-- Hose and sediment trap from inlet of gas valve
-- Screws securing valve bracket to heater base.
-- Burner bolt from underside of base.
-- Screws and spacers securing burner casting to
heat chamber.
2. Remove control valve with burner from heater. Rotate
the valve/manifold assembly as necessary so orifice
and orifice block can exit the burner casting venturi
port..
3. Replace components as needed.
15
WARNING
Fire Hazard
FIG. 12
SWITCH W/ PADDLE
HOUSING SIDE
PANEL
LEADS
3. Within a minute, you should hear a pop coming
from the switch, which indicates the contacts of the
switch have opened.
4. Allow the switch cool down for about a minute
before firmly pressing the red reset button on the
switch.
5. Check for electrical continuity across the switch
terminals to make sure the contacts have closed.
6. Reinstall the switch back into the heater.
FIG. 13
RESET BUTTON
TERMINAL
MOUNTING
LEG
FIG. 14
GAS CONTROL
VALVE
NUTS
PADDLE
OBLONG HOLE
SENSING
SURFACE
FLAME
ORIFICE
BLOCK
BURNER
ORIFICE