Bryant 340AAV Installation, Start-Up, And Operating Instructions Manual page 51

d. Find installation altitude in Table 14 or 15.
NOTE: For Canada altitudes of 2001 to 4500 ft, use U.S.A.
altitudes of 2001 to 3000 ft (610 to 914 M) in Table 14 or 15.
e. Find closest natural gas heat value and specific gravity
on Table 14 or 15.
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 (0 - - 610 M) altitude using Table 14)
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.
b. Remove cap that conceals adjustment screw for gas
valve regulator. (See Fig. 48.)
c. Jumper R and W thermostat connections on control to
start furnace.
d. 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
(610 M). For altitudes above 2000 ft (610 M), the manifold
pressure can be adjusted from 2.0 in. wc to 3.8 in. wc. If manifold
pressure is outside this range, change burner orifices to obtain
pressure in this range.
CAUTION
!
UNIT DAMAGE HAZARD
Failure to follow this caution may result in reduced
furnace life.
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.
e. Replace gas valve regulator adjustment screw cap.
f. Replace burner enclosure front and verify adjusted gas
input rate using method outlined in item 3.
CAUTION
!
UNIT DAMAGE HAZARD
Failure to follow this caution may result in component damage
due to flame impingement of burners and heat exchangers.
DO NOT redrill orifices. Improper drilling (burrs,
out-of-round holes, etc.) can cause excessive burner noise
and misdirection of burner flames. (See Fig. 49.)
g. Look through sight glass in burner enclosure and
check burner flame. Burner flame should be clear blue,
almost transparent. (See Fig. 50.)
h. Remove jumper from R and W.
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.
a. Calculate high-altitude adjustment (if required).
UNITED STATES
At altitudes above 2000 ft (610 M), this furnace has
been approved for a 2% derate for each 1000 ft (305 M)
above sea level. See Table 16 for derate multiplier
factor.
EXAMPLE: 100,000 BTUH INPUT FURNACE INSTALLED AT
4300 FT.
Furnace Input Rate X
at Sea Level
100,000 X
CANADA
At installation altitudes from 2001 to 4500 ft (610 to
1372 M), this furnace must be derated 5% by an
authorized Gas Conversion Station or Dealer. To
determine correct input rate for altitude, see example
above and use 0.95 as derate multiplier factor.
b. Reinstall burner box cover.
c. Gas valve regulator seal cap MUST be on.
d. Turn off all other gas appliances and pilots.
e. Start furnace and let operate for 3 minutes.
f. Measure time (in sec) for gas meter test dial to
complete 1 revolution.
g. Refer to Table 17 for cu ft of gas per hr.
h. Multiply gas rate (cu ft/hr) X heating value (Btu/cu ft)
using natural gas heating value from local gas
utility/supplier.
- - 51 - -
Derate = Furnace Input
Multiplier Rate at
Factor Installation
Altitude
0.91 = 91,000