Bryant Gas Air 393U - Manual (Page 11)

Light Main Burners using the procedure contained on
the metal Lighting Instruction Plate attached to the
front of the furnace.
Adjust Gas Rate. Set the room thermostat on call
for heat and adjust the gas rate as follows:
1. City Gases - Measure gas input at the meter.
The burners are equipped with fixed orifices, sized
to produce the rated input shown on the rating plate.
If measured and rated input are not approximately
the same, the gas pressure regulator may be adjusted
as follows:
a. To increase input: Turn pas pressure regu­
lator adjusting screw ‘clockwise’. (Adjusting screw
is concealed under the regulator sealing cap).
b. To decrease input: Turn the adjusting screw
‘counter-clockwise’. The manifold pressure should
be set as follows:
Manufactured Gas - 3 inches w.c.
Natural Gas - 3 inches w.c.
Maximum pressure departure from recommended pres­
sure should be plus or minus 0.3 inches w.c.
2. LP Gas - LP gas units are not equipped with
gas pressure regulators. Burner orifices are sized
to give the rated input at a manifold pressure of
11 inches w.c. Since meters are not normally used
with LP gas, it will be necessary in most cases to
check the manifold pressure and adjust the regulator
at the supply tank to provide a pressure of 11 inches
w.c.
3. If the input in item (1) or (2) above is too great
or too little, install new orifices or re-drill the
existing orifices (whichever is necessary) to obtain
the rated input. Be sure the rated input is obtained
without any appreciable change in manifold gas
pressure.
Adjust Main Burner Flame — The main burner flame
should be clear blue, almost transparent, with a well-
defined inner cone. If there is insufficient primary
air, the flame will be yellow-tipped. If there is too
much primary air the flame will be well-defined, but
with a tendency to dance or lift off the burner ports.
1. Allow furnace to operate 15 minutes.
2. Adjust each burner by closing the air shutter
until a slight yellow tip appears on the flame; then
open the air shutter just enough to clear the yellow
from the flame.
CHECK CONTROLS
Bryant Diaphragm Gas Control Valve —if not already
checked when lighting the main burner, check the
proper operation of this valve by moving the room
thermostat pointer above and below room temperature
and observe that the main burners light on call for
heat and go off when the pointer is moved below the
room temperature setting. However, there will be
approximately a 30 second delay on ignition and
extinction.
Automatic Pilot - To check the pilot operation
follow the instructions below:
1. Set the room thermostat on call for heat.
There is a delay before burners light.
2. After burners have lit, shut off the pilot gas
valve.
3. The automatic pilot will break the electrical
circuit to the gas valve and the burners will shut off.
Limit Control - This control functions to shut off
the gas if the furnace becomes over-heated. The
method of checking satisfactory operation is left to
the discretion of the installer. Extreme caution
should always be employed.
Blower Adjustment - It is important that the blower
speed be adjusted before there is any attempt to
adjust the fan control switch.
The blower speed is set at the factory. Under no
circumstances should the temperature rise across
the furnace be allowed to exceed 105 degrees F
on all sizes except the size 50. On the size 50,
the temperature rise must not be allowed to exceed
70 degrees F. After the desired air flow or tempera­
ture rise across the furnace has been obtained, the
installation should be complete. However, it may be
necessary to change the factory setting on the Fan
Control Switch. This may be done as described
under the discussion on controls.
393U
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