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5. Remove funnel and tube from inducer housing and replace
drain connection cap and clamp.
III. PURGE GAS LINES
If not previously done, purge lines after all connections have been
made and check for leaks.
WARNING: Never purge a gas line into a combustion
chamber. Never use matches, candles, flame, or other
sources of ignition for purpose of checking leakage. Use
a soap-and-water solution to check for leakage. Failure to
follow this warning could result in fire, explosion, per-
sonal injury, or death.
IV. ADJUSTMENTS
A. Set Gas Input Rate
Furnace gas input rate on rating plate is for installations at altitudes
up to 2000 ft. Furnace input rate must be within ±2 percent of input
on furnace rating plate.
1. Determine natural gas orifice size and manifold pressure for
correct input.
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. Table 7 can only be used for
model 345MAV furnaces.
d. Find installation altitude in Table 7.
NOTE: For Canada altitudes of 2000 to 4500 ft, use U.S.A.
altitudes of 5001 to 6000 ft in Table 7.
e. Find closest natural gas heat value and specific gravity
on Table 7.
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 altitude)
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.
a. Remove burner enclosure front.
→ Fig. 38—Inducer Housing Drain Tube
A99118
→ Fig. 39—Filling Condensate Trap
A99119
—33—