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14. Combustion Air Inducer
Prove Switch (S18)
G60UHV(X) series units are equipped with a dual combus-
tion air proving switch (first and second stage) located on
the combustion air inducer orifice bracket. The switch is con-
nected to the combustion air inducer housing by means of a
flexible silicone hose. It monitors negative air pressure in the
combustion air inducer housing.
The switches are a single-pole single-throw proving switch
electrically connected to the furnace control. The purpose of
the switch is to prevent burner operation if the combustion
air inducer is not operating or if the flue becomes obstructed.
On heat demand (first or second stage) the switch senses
that the combustion air inducer is operating. It closes a cir-
cuit to the furnace control when pressure inside the com-
bustion air inducer decreases to a certain set point.
Set points vary depending on unit size. See tables 26, 27
and 28. The pressure sensed by the switch is negative rela-
tive to atmospheric pressure. If the flue becomes ob-
structed during operation, the switch senses a loss of neg-
ative pressure (pressure becomes more equal with atmo-
spheric pressure) and opens the circuit to the furnace con-
trol and gas valve. A bleed port on the switch allows rela-
tively dry air in the vestibule to purge switch tubing, to pre-
vent condensate build up.
The switch is factory set and is not field adjustable. It is a
safety shut-down control in the furnace and must not be by−
passed for any reason. If switch is closed or by−passed, the
control will not initiate ignition at start up.
G60UHV(X) Unit
−070
−090
−110
−135
G60UHV(X) Unit
−070
−090
−110
−135
*Unit requires conversion kit at this altitude. See High Altitude table.
G60UHV(X) Unit
−070
−090
−110
−135
*Unit requires conversion kit at this altitude. See High Altitude table.
Page 31
TABLE 26
0' to 4500'
Set Point High
Set Point Low
Heat
Heat
0.40"
0.20"
0.45"
0.20"
0.50"
0.20"
0.50"
0.20"
TABLE 27*
4501' to 7500'
Set Point High
Set Point Low
Heat
Heat
0.40"
0.20"
0.40"
0.20"
0.45"
0.20"
0.45"
0.20"
TABLE 28*
7501' to 10,000'
Set Point High
Set Point Low
Heat
Heat
0.35"
0.20"
0.35"
0.20"
0.40"
0.20"
0.40"
0.20"
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