SERVICING
37
CHECKING ORIFICES
A/GMVC, A/GCVC model furnaces have factory installed
#45 natural gas orifices.
The only time resizing is required is when a reduction in
firing rate is required for an increase in altitude or a furnace
is being converted for use with L.P. gas.
Orifices should be treated with care in order to prevent
damage. They should be removed and installed with a box-
end wrench in order to prevent distortion. In no instance
should an orifice be peened over and re-drilled. This will
change the angle or deflection of the vacuum effect or
entraining of primary air, which will make it difficult to adjust
the flame properly. This same problem can occur if an
orifice spud of a different length is substituted.
WARNING
Disconnect ALL gas and electrical power supply.
1.
Check orifice visually for distortion and/or burrs.
2.
Check orifice size by the number stamped on the orifice.
A
GAS
STREAM B
The length of Dimension “A” determines the angle of Gas
Stream “B”.
DENT OR
BURR
GAS
STREAM B
A dent or burr will cause severe deflection of the gas
stream.
CHECKING GAS PRESSURE
Gas Supply Pressure Measurement
CAUTION
To prevent unreliable operation or equipment
damage, the inlet gas supply pressure must
be as specified on the unit rating plate with
all other household gas fired appliances
operating.
Gas inlet and manifold pressures should be checked and
adjusted in accordance to the type of fuel being consumed.
The line pressure supplied to the gas valve must be within
the range specified below. The supply pressure can be
measured at the gas valve inlet pressure tap or at a hose
fitting installed in the gas piping drip leg. The supply
pressure must be measured with the burners operating.
To measure the gas supply pressure, use the following
procedure.
WARNING
Disconnect electrical power and shut off gas
supply.
1. After turning off gas to furnace at the manual gas
shutoff valve external to the furnace, remove burner
compartment door to gain access to the gas valve.
2. Connect a calibrated water manometer (or appropriate
gas pressure gauge) at either the gas valve inlet
pressure tap or the gas piping drip leg as shown in the
following figures.
NOTE: At either location, a hose fitting must be
installed prior to making the hose connection.
NOTE: Use adapter kit #0151K00000S to measure
gas pressure on White-Rodgers 36J54 gas valves.
3. Turn ON the gas and electrical power supply and operate
the furnace and all other gas consuming appliances on
the same gas supply line.
4.
Measure furnace gas supply pressure with burners firing.
Supply pressure must be within the range specified in
the following table.
Inlet Gas Supply Pressure
Natural Gas
Minimum: 4.5” w.c. Maximum: 10.0” w.c.
Propane Gas
Minimum: 11.0” w.c. Maximum: 13.0” w.c.
If supply pressure differs from above, make necessary
adjustments to pressure regulator, gas piping size, etc.,
and/or consult with local gas utility.
