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Adjusting Gas Input
Gas input of the furnace and each chiller must be
checked and adjusted if necessary to agree with that
shown on the rating plates. The burners are equipped
with fixed orifices.
CAUTION: The chillers may be run for short periods
with the panels removed. Prolonged operation with
panels removed should be avoided.
Natural gas units are equipped with adjustable gas
pressure regulators. Propane gas units are not equip¬
ped with a pressure regulator.
One of the following two methods may be used to
check natural gas input on both the furnace and
chillers.
A. Measuring Gas Flow at Meter
All gas appliances must be turned off except the bur¬
ners on the manifold being checked when measuring
the gas flow at the meter to adjust the gas input.
Proceed as follows:
1. Determine the number of seconds required for the
gas meter test dial to complete one revolution.
2. Divide 3600 by the number of seconds in Step 1.
3. Multiply the result in Step 2 by the number of
cubic feet of gas flow per hour.
4. Multiply the result of Step 3 by the Btu heating
value of the gas (consult local utility for value). This
is the total measured Btu/hr input.
Compare this value with the one shown on the rating
plate.
Example: Suppose the size of the test dial is 5 cu. ft.;
it takes 40 seconds for the dial to complete one
revolution; heating value of the gas is 1050 Btu/cu. ft.
Proceed as follows:
40 seconds to complete one revolution
3600 divided 40 equals 90
90 x 5 - 450 cu. ft. per hour of gas flow
450 x 1050 - 472,5000 Btuh input
Only minor changes should have to be made at the
pressure regulator to bring it within the rated input of
the unit. If the manifold pressure must be changed
more than
0.3" w.c. to obtain the rated input, the
orifices should be changed accordingly.
B. Using Water Manometer
Proceed as follows when using a water manometer to
measure the manifold pressure when adjusting the gas
input:
1. Connect a water manometer to the 1/8" pressure
tap on the manifold or gas valve.
2. With the burners fired, set the correct manifold
pressure as shown in Table IV. Check with the gas
utility for the Btu valve and specific gravity of gas in
the area.
TABLE IV—MANIFOLD PRESSURE
(Inches w.c.)
Specific Gravity
0.59
0.61
0.63
0.65
0.67
900
3.9"
4.0"
4.1"
4.2"
4.3"
950
3.5"
3.6"
3.7"
3.8"
3.9"
1000
3.1"
3.2"
3.3"
3.4"
3.5"
1025
3.0"
3.1"
3.2"
3.3"
3.4"
1050
2.8"
2.9"
3.0"
3.1"
3.2"
1100
2.6"
2.7"
2.8"
2.9"
3.0"
Adjusting Pressure Regulator
If the measured
and rated input are not ap¬
proximately the same, the gas pressure regulator may
be adjusted as follows:.
To increase input. Remove regulator sealing cap
and turn gas pressure regulator adjusting screw
clockwise.
To decrease input. Remove regulator sealing cap and
turn gas pressure adjusting screw counterclockwise.
Checking Propane Gas Input
The burner orifices are sized for rated input with a
manifold pressure of 11.0" w.c. for propane gas. Con¬
nect a manometer of the 1/8" pressure tap on the
chiller manifold gas valve. With the burners fired, ad¬
just regulator at the supply tank to provide a pressure
of 11.0" w.c. Check manifold pressure of each chiller.
Check the furnace manifold pressure to see that it is
also 11.0 inches w.c.
Burner Adjustment
To adjust the primary air to each burner, partially
close the air shutter until there is a slight yellow tip at
the top of each flame, then open the air shutter until
the yellow tip just disappears. This should be done af¬
ter the burners have been operating at full input for 5
minutes.
VIII. FURNACE OPERATION
In order to check the furnace for proper performance,
the following sequence of control operation is given.
CAUTION: The pilot valve and main burner manual
valve must be closed for at least five minutes before
starting the furnace.
1. Set the thermostat system switch to "heat", set the
fan switch to "auto" and set the thermostat below
room temperature.
2. Turn on electrical power to the unit.
3. Open pilot gas valve. Gas will flow to the pressure
switch and to the pilot. The electrical contacts in the
pressure switch close, energizing the reignition coil
which ignites the pilot gas. (Natural gas only; pilots
on propane unit must be lighted manually per instruc¬
tion on rating plate.)
The pilot flame causes the monometal contacts in the
Bryant 733 pilot to "Break" the re-ignition coil circuit
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