Bryant 355BAV Installation, Start-Up, And Operating Instructions Manual page 38

Fig. 41 - - Inducer Housing Drain Tube
Fig. 42 - - Filling Condensate Trap
Table 10 – Blower Off Delay Setup Switch Position
DESIRED
HEATING MODE
BLOWER OFF
DELAY (SEC)
90
120
150
180
1. Inducer Prepurge Period- -The furnace control CPU turns
on inducer motor IDM and slowly increases the inducer
motor speed. When the low- -heat pressure switch LPS
closes, inducer motor RPM is noted by the furnace control
CPU, and a 25- -sec. prepurge period begins. The RPM is
used to evaluate vent system resistance. This evaluation is
then used to determine the required RPM necessary to oper-
ate the inducer motor during the low- -heat prepurge period
and low- -heat mode.
NOTE: The heat cycle can start in either high- -or low- -heat. If a
high- -heat cycle is initiated, the furnace control CPU will
deenergize the high- -heat pressure switch relay HPSR to close the
NC contact and continues to increase the inducer motor speed after
the low- -heat pressure switch LPS closes. When the high- -heat
pressure switch closes, inducer motor RPM is noted by the furnace
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control CPU before the 25- -sec prepurge period begins. The RPM
is used to evaluate vent system resistance. This evaluation is then
used to determine the required RPM necessary to operate the
inducer motor in high- -heat mode.
2. Igniter Warm- -Up- -At end of the prepurge period, the Hot
Surface Igniter HSI is energized for a 17- -sec igniter warm- -
up period.
3. Trial- -For- -Ignition Sequence- -When the igniter warm- -up
period is completed, the main gas valve relay contacts GVR
close to energize the gas valve GV, the gas valve opens. The
gas valve GV permits gas flow to the burners where it is
ignited by the Hot Surface Igniter HSI. Five seconds after
the GVR closes, a 2- -second flame period begins. The HSI
igniter will remain energized until the flame is sensed or un-
til the 2- -second flame proving period begins.
If the furnace control CPU selects high- -heat operation, the
high- -heat gas valve solenoid GV- -HI is also energized.
4. Flame- -Proving- -When burner flame is proved at the flame
proving sensor electrode FSE, the furnace control CPU be-
gins the blower- -ON delay period and continues to hold the
gas valve GV- -M open. If the burner flame is not proved
within two seconds, the control CPU will close the gas
valve GV- -M, and the furnace control CPU will repeat the
ignition sequence for up to three more Trials- -For- -Ignition
before going to Ignition- -Lockout. Lockout will be reset
automatically after three hours, by momentarily interrupting
115 vac power to the furnace, or by interrupting 24 vac
power at SEC1 or SEC2 to the furnace control CPU (not at
W/W1, G, R, etc.).
If flame is proved when flame should not be present, the
furnace control CPU will lock out of Gas- -Heating mode
and operate the inducer motor IDM on high speed until
flame is no longer proved.
5. Inducer Speed Change- -If the cycle starts in low- -heat, the
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furnace control CPU reduces the inducer speed slightly after
flame sense. If cycle starts in high- -heat, the furnace control
CPU increases the inducer speed 15 seconds after flame
sense. The reduction in speed in low- -heat is to optimize
combustion for maximum efficiency.
6. Blower- -On delay- -If the burner flame is proven, the
blower- -ON delay for low- -heat and high- -heat are as fol-
38
SETUP SWITCH
(SW1---7 AND SW1---8) POSITION
SW1--- 7 SW1--- 8
OFF OFF
ON OFF
OFF ON
ON ON