Lennox G50UHi Unit Information page 15

A proving switch connected to the combustion air inducer ori-
fice plate is used to prove inducer operation. The combustion
air inducer orifice will be different for each model. See table
10 for orifice sizes. The switch monitors air pressure in the in-
ducer housing. During normal operation, the pressure in the
housing is negative. If pressure becomes less negative (sig-
nifying an obstruction) the proving switch opens. When the
proving switch opens, the furnace control (A92) immediately
closes the gas valve to prevent burner operation.
TABLE 10
G50UHi Unit
−070
−090
−110
−135
Horizontal Applications
The G50UHi furnace can be installed in horizontal applica-
tions.
The combustion air inducer may be rotated clockwise or
counterclockwise by 90° to allow for vertical vent discharge
in a horizontal application. Remove the four mounting
screws, rotate the assembly (assembly consists of orifice
plate, proving switch, gasket and combustion air inducer),
then reinstall the mounting screws. See figure 14. Use the
provided wire tie to bundle the pressure switch wires with
the inducer motor power leads. Route the wires away
from moving parts and the heat of the inducer motor to
prevent damage to the wires. Use sheet metal shears to
remove the cut out from the side of the cabinet. See figure
15. Use the two provided sheet metal screws to install the
cut out on the top cap to cover the original flue outlet open-
ing.
Combustion Air Inducer
90°
(Upflow Position)
Flue Transition
(Do not remove
)
Mounting Screws
(Remove)
FIGURE 14
C.A.I. Orifice Size
1 7/16"
1 11/16"
2 5/32"
2 3/8"
90°
MOUNTING SCREWS
(Remove)
Power Leads
Page 15
Optional Flue Outlet
(Horizontal Installation)
Top Cap
Flue Outlet Hole
Reattach
(
Cutout Here)
Cut out
FIGURE 15
10. Flame Rollout Switches (S47)
Flame rollout switch is a high temperature limit located on
top of the burner box (135 and 155 Btuh units− rollout
switches are located on the inner sides of burner box).
Each furnace is equipped with two identical switches. One
switch is located over the far left burner and the other
switch is located over the far right burner. The limit is a N.C.
SPST manual-reset limit connected in series with the igni-
tion control A92. When S47 senses rollout, the ignition con-
trol immediately stops ignition and closes the gas valve. If
unit is running and flame rollout is detected, the gas valve
will close and ignition control will be disabled. Rollout can
be caused by a blocked heat exchanger, flue or lack of
combustion air. The switch is factory set and cannot be ad-
justed. See table 11. The switch can be manually reset. To
manually reset a tripped switch, push the reset button located
on the control.
TABLE 11
BTUH INPUT
−070
−090
−110
−135
Top View of Furnace
Supply Air
Opening
Optional
Flue Outlet
Rollout Switch Setpoint
250° F
200° F