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1. Determine natural gas orifice size and manifold pressure for
correct input.
a. Obtain average gas heat value (at installed altitude) from
local gas supplier.
b. Obtain average gas specific gravity from local gas
supplier.
c. Verify furnace model and size. Table 9 can only be used
for model 340MAV furnaces with heating sizes of 040
through 120. Table 10 can only be used for model
340MAV furnaces with a heating size of 140.
d. Find installation altitude in Table 9 or 10.
NOTE: For Canada altitudes of 2000 to 4500 ft, use U.S.A.
altitudes of 2001 to 3000 ft in Table 9 or 10.
e. Find closest natural gas heat value and specific gravity in
Table 9 or 10.
f. Follow heat value and specific gravity lines to point of
intersection to find orifice size and manifold pressure
settings for proper operation.
Fig. 49—Filling Condensate Trap
A99119
Fig. 48—Inducer Housing Drain Cap
A99118
Fig. 50—Redundant Automatic Gas Valve
A03142
REGULATOR
SEAL CAP
REGULATOR
ADJUSTMENT
SCREW
REGULATOR SPRING
(PROPANE - WHITE, 6 TURNS
NATURAL - SILVER, 10 TURNS)
GAS PRESSURE
REGULATOR
ADJUSTMENT
MANIFOLD
PRESSURE TAP
INLET
PRESSURE TAP
ON/OFF SWITCH
Fig. 51—Burner Orifice
CAUTION: DO NOT redrill orifices. Improper drilling
(burrs, out-of-round holes, etc.) can cause excessive
burner noise and misdirection of burner flames. This can
result in flame impingement of burners and heat exchang-
ers causing failures. (See Fig. 51.)
A93059
BURNER
ORIFICE
—37—
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