Bryant Preferred 581J04-14, Service And Maintenance Instructions, Page: 28 / 148

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GAS HEATING SYSTEM
General
The heat exchanger system consists of a gas valve feeding mul-
tiple in-shot burners off a manifold. The burners fire into
matching primary tubes. The primary tubes discharge into
combustion plenum where gas flow converges into secondary
tubes. The secondary tubes exit into the induced draft fan
wheel inlet. The induced fan wheel discharges into a flue pas-
sage and flue gases exit out a flue hood on the side of the unit.
The induced draft fan motor includes a flue gas pressure switch
circuit that confirms adequate wheel speed through the Inte-
grated Gas Control (IGC) board. Safety switches include a
Rollout Switch (at the top of the burner compartment) and a
limit switch (mounted through the fan deck, over the tubes).
(See Fig. 46 and 47.)
Fig. 46 — Burner Section Details
Fig. 47 — Limit Switch Location
Fuel Types and Pressures
NATURAL GAS
The 581J unit is factory-equipped for use with natural gas
(NG) fuel at elevation under 2000 ft (610 m). See section “Ori-
fice Replacement” for information in modifying this unit for
installation at elevations above 2000 ft (610 m).
Gas line pressure entering the unit’s main gas valve must be
within specified ranges (see Table 8). Adjust unit gas regulator
valve as required or consult local gas utility.
Manifold pressure is factory-adjusted for NG fuel use. Adjust
as required to obtain best flame characteristic. See Table 9.
NA: Not Available
†3 Phase models only
LIQUID PROPANE
See Tables 10 and 11.
Accessory packages are available for field-installation that will
convert the 581J unit (except low NOx model) to operate with
liquid propane (LP) fuels. These kits include new orifice spuds,
new springs for gas valves and a supply line low pressure
switch. See section on Orifice Replacement for details on ori-
fice size selections.
Low NOx models include specially-sized orifices and use of dif-
ferent flue flow limits and tube baffles. Because of these extra
features, conversion of these models to LP is not recommended.
Fuel line pressure entering unit gas valve must remain within
specified range.
Manifold pressure for LP fuel use must be adjusted to specified
range. Follow instructions in the accessory kit to make initial
readjustment.
NA: Not Available
SUPPLY PRESSURE SWITCH
The LP conversion kit includes a supply low pressure switch.
The switch contacts (from terminal C to terminal NO) will
open the gas valve power whenever the supply line pressure
drops below the set point. See Fig. 48 and 49. If the low pres-
sure remains open for 15 minutes during a call for heat, the
IGC circuit will initiate a Ignition Fault (5 flashes) lockout. Re-
set of the low pressure switch is automatic on rise in supply
line pressure. Reset of the IGC requires a recycle of unit power
after the low pressure switch has closed.
This switch also prevents operation when the propane tank lev-
el is low, which can result in gas with a high concentration of
impurities, additives, and residues that have settled to the bot-
tom of the tank. Operation under these conditions can cause
harm to the heat exchanger system. Contact your fuel supplier
if this condition is suspected.
INDUCED-
DRAFT
MOTOR
MOUNTING
PLATE
INDUCED-
DRAFT
MOTOR
MANIFOLD
PRE
SS URE
TAP
VE S TIBULE
PLATE
FLUE
EXHAU
S T
ROLLOUT
S WITCH
BLOWER
HOU
S ING
GA S
VALVE
BURNER
S ECTION
Limit S witch
for S ide s hot
Limit S witch
for Down s hot
Table 8 — Natural Gas Supply Line Pressure Ranges
UNIT
MODEL
UNIT
SIZE
MIN MAX
581J All 4.0 in. wg (996 Pa) 13.0 in. wg (3240 Pa)
Table 9 — Natural Gas Manifold Pressure Ranges
UNIT
MODEL
UNIT
SIZE
HIGH FIRE LOW FIRE RANGE
581J All 3.5 in. wg
(872 Pa)
1.7 in. wg
(423 Pa)†
2.0-5.0 in. wg (Hi)
(498-1245 Pa)
581J Low
NOx
04,
05, 06
3.5 in. wg
(872 Pa)
NA
2.0-5.0 in. wg (Hi)
(498-1245 Pa)
Table 10 — Liquid Propane Supply Line Pressure Ranges
UNIT MODEL UNIT SIZE MIN MAX
581J All
11.0 in. wg
(2740 Pa)
13.0 in. wg
(3240 Pa)
Table 11 — Liquid Propane Manifold Pressure Ranges
UNIT MODEL UNIT SIZE MIN MAX
581J All
11.0 in. wg
(2740 Pa)
13.0 in. wg
(3240 Pa)