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11. Primary Limit Control (S10)
The primary limit (S10) on G50UHi units is located in the heat-
ing vestibule panel. When excess heat is sensed in the heat
exchanger, the limit will open. If the limit is open, the furnace
control energizes the supply air blower and closes the gas
valve. The limit automatically resets when unit temperature re-
turns to normal. The switch must reset within three minutes or
SureLight board will go into Watch guard for one hour. The
switch is factory set and cannot be adjusted. The switch may
have a different setpoint for each unit model number. If limit
switch must be replaced, see Lennox Repair Parts hand-
book.
12. Secondary Limit Controls (S21)
The secondary limit (S21) on G50UHi units is located in the
blower compartment in the back side of the blower housing.
See figure 13. Table 12 and the blower speed chart on the wir-
ing diagram show secondary limit quantities per unit. When
excess heat is sensed in the blower compartment, the limit will
open. If the limit is open, the furnace control energizes the sup-
ply air blower and closes the gas valve. The limit automatically
resets when unit temperature returns to normal. G50UHi−1
through −6 units use a surface type limit, factory set to open at
125°F. G50UHi −7 and later units use an air stream limit fac-
tory set to open at 135°. The secondary limit cannot be ad-
justed.
TABLE 12
G50UHi
UNIT
Quantity
LeftSide
Right Side
36A−070
2
Yes
Yes
36B−090
1
No
Yes
48B−090
2
Yes
Yes
60C−110
1
No
Yes
60D−135
2
Yes
Yes
13. Gas Valve (GV1) Figures 16, 17 & 18
The G50UHi uses a gas valve manufactured by Honeywell
or White Rodgers. The valve is internally redundant to as-
sure safety shut−off. If the gas valve must be replaced, the
same type valve must be used.
24VAC terminals and gas control knob or switch are located
on the valve. All terminals on the gas valve are connected to
wires from the electronic ignition control. 24V applied to the ter-
minals energizes the valve.
Inlet and outlet pressure taps are located on the valve. A regu-
lator adjustment screw is located on the valve.
LPG changeover kits are available from Lennox. Kit s include
burner orifices and a gas valve regulator conversion kit.
WHITE RODGERS 36E SERIES GAS VALVE
GAS VALVE SHOWN IN OFF POSITION
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
MANIFOLD
PRESSURE
OUTLET
Summary of Contents for G50UHi Series
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