Bryant D Series Installation, Start-Up, And Operating Instructions Manual page 37

Fig. 47—Inducer Housing Drain Tube
a. Obtain average yearly heat value (at installed altitude)
from local gas supplier.
b. Obtain average yearly specific gravity from local gas
supplier.
c. Verify furnace model and size. Table 8 can only be used
for model 350MAV furnaces with heating sizes of 040
through 120. Table 9 can only be used for model
350MAV furnaces with a 140 heating size.
d. Find installation altitude in Table 8 or 9.
NOTE: For Canada altitudes of 2000 to 4500 ft, use U.S.A.
altitudes of 2001 to 3000 ft in Table 8 or 9.
e. Find closest natural gas heat value and specific gravity
on Table 8 or 9.
f. Follow heat value and specific gravity lines to point of
intersection to find orifice size and manifold pressure
settings for proper operation.
EXAMPLE: (0—2000 ft altitude using Table 8)
Heating value = 1050 Btu/cu ft
Specific gravity = 0.62
Therefore: Orifice No. 45
Manifold pressure 3.6-in. wc
* Furnace is shipped with No. 45 orifices. In this example
all main burner orifices are the correct size and do not need
to be changed to obtain the proper input rate.
Check and verify burner orifice size in furnace. NEVER ASSUME
ORIFICE SIZE; ALWAYS CHECK AND VERIFY.
2. Adjust manifold pressure to obtain input rate.
NOTE: Manifold pressure must always be measured with burner
enclosure front REMOVED. Gas meter must always be clocked
with burner enclosure front INSTALLED.
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Fig. 48—Filling Condensate Trap
a. Remove burner enclosure front.
b. Remove cap that conceals adjustment screw for gas
valve regulator. (See Fig. 49.)
c. Turn adjusting screw, counterclockwise (out) to decrease
manifold pressure or clockwise (in) to increase manifold
pressure.
NOTE: This furnace has been approved for a manifold pressure
of 3.2 in. wc to 3.8 in. wc when installed at altitudes up to 2000 ft.
For altitudes above 2000 ft, the manifold pressure can be adjusted
from 2.0 in. wc to 3.8 in. wc.
CAUTION: DO NOT bottom out gas valve regulator
adjusting screw. This can result in unregulated manifold
pressure and result in excess overfire and heat exchanger
failures.
NOTE: If orifice hole appears damaged or it is suspected to have
been redrilled, check orifice hole with a numbered drill bit of
correct size. Never redrill an orifice. A burr-free and squarely
aligned orifice hole is essential for proper flame characteristics.
d. Replace gas valve regulator adjustment screw cap.
e. Replace burner enclosure front and verify adjusted gas
input rate using method outlined in item 3.
f. Look through sight glass in burner enclosure and check
burner flame. Burner flame should be clear blue, almost
transparent. (See Fig. 50.)
3. Verify natural gas input rate by clocking gas meter.
NOTE: Be sure all pressure tubing, combustion-air and vent
pipes, and burner enclosure front are in place when checking input
by clocking gas meter.
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