Page 16
FIGURE 11
G40DF−1, −2 UNITS
WITHOUT SHIELD
G40DF UNITS
WITH SHIELD
11.Secondary Limit Controls (S21)
The secondary limit (S21) is an air stream type limit located in
the blower compartment in the back side of the blower hous-
ing. See figure 12. When excess heat is sensed in the blower
compartment, 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. G40DF−1 through −6 units use a 3/4" diameter
limit factory set to open at 150°. G40DF−7 and later units, use
a 1/2" diameter limit factory set to open at 135 °.
FIGURE 12
SUPPLY AIR BLOWER AND SECONDARY LIMIT
SECONDARY
LIMIT
CAPACITOR
MOTOR/BLOWER
ASSEMBLY
To Remove Blower From Unit: Disconnect Power, Remove Control
Box, Remove flue pipe, Remove Bolts and Unplug Motor Wires
From Control Board. Then Slide Out Front of Unit.
12.Gas Valve Figures 13, 14, 15 & 16
The G40DF(X) uses a gas valve manufactured by Honey-
well or White Rodgers. The valve is internally redundant to
assure 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. Kits 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
FIGURE 13
FIGURE 14
WHITE RODGERS 36F Series Gas Valve
GAS VALVE SHOWN IN OFF POSITION
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
MANIFOLD
PRESSURE
OUTLET
ON
OFF
HONEYWELL VR8205 SERIES GAS VALVE
GAS VALVE SHOWN IN OFF POSITION
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
MANIFOLD
PRESSURE
OUTLET
FIGURE 15
HONEYWELL VR8205 SERIES GAS VALVE
(With On/Off Switch)
GAS VALVE ON/OFF SWITCH SHOWN IN ON POSITION
MANIFOLD
PRESSURE
OUTLET
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
(under cap)
FIGURE 16