GC9C96 Service Manual
SYSTEM OPERATION
8
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This furnace is shipped from the factory congured for natural
gas at standard altitude. Propane gas installations require
an orice change to compensate for the energy content
dierence between natural and propane gas.
High altitude installations may require both a pressure switch
and an orice change. These changes are necessary to
compensate for the natural reduction in the density of both
the gas fuel and the combustion air at higher altitude.
Refer to the product Specication Sheet for a listing of
appropriate manufacturer’s kits for propane gas and/or high
altitude installations. The indicated kits must be used to insure
safe and proper furnace operation. All conversions must be
performed by a qualied installer, or service agency.
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A condensing gas furnace achieves its high level of eciency
by extracting almost all of the heat from the products of
combustion and cooling them to the point where condensation
takes place. The condensate which is generated must be
piped to an appropriate drain location.
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• • If the drain line is routed through an area which may
see temperatures near or below freezing, precautions
must be taken to prevent condensate from freezing
within the drain line.
• • If an air conditioning coil is installed with the furnace,
a common drain may be used. An open tee must
be installed in the drain line, near the cooling coil, to
relieve positive air pressure from the coil’s plenum.
This is necessary to prohibit any interference with the
function of the furnace’s drain trap.
The furnace rating plate includes the approved furnace gas
input rating and gas types. The furnace must be equipped
to operate on the type of gas applied. This includes any
conversion kits required for alternate fuels and/or high altitude.
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Inlet gas supply pressures must be maintained within the
ranges specied below. The supply pressure must be constant
and available with all other household gas red appliances
operating. The minimum gas supply pressure must be
maintained to prevent unreliable ignition. The maximum must
not be exceeded to prevent unit overring.
Natural Gas Minimum: 4.5" w.c. Maximum: 10.0" w.c.
Propane Gas Minimum: 11.0" w.c. Maximum: 13.0" w.c.
When this furnace is installed at high altitude, the appropriate
High Altitude orice kit must be applied. This is required due
to the natural reduction in the density of both the gas fuel and
combustion air as altitude increases. The kit will provide the
proper design certied input rate within the specied altitude
range.
High altitude kits are purchased according to the installation
altitude and usage of either natural or propane gas. Refer
to the product Specication Sheet for a tabular listing of
appropriate altitude ranges and corresponding manufacturer’s
high altitude (Natural, Propane gas, and/or Pressure Switch)
kits.
Do derate the furnace by adjusting the manifold pressure
to a lower pressure than specied on the furnace rating plate.
The combination of the lower air density and a lower manifold
pressure will prohibit the burner orice from drawing the proper