Sequence Of Operation; Two-Stage Heating With Single-Stage Thermostat (Adaptive Mode) - Bryant 352MAV Installation, Start-Up, And Operating Instructions Manual

OPEN STAND
PIPE FOR
A/C OR
HUMIDIFIER
DRAIN
TEE
TO OPEN
DRAIN
Fig. 48—Example of Field Drain Attachment
CONDENSATE TRAP
WIRE TIE(S)
HEAT TAPE
(3 WRAPS MINIMUM)
Fig. 49—Condensate Trap Heat Tape
CAUTION: This furnace is equipped with a manual
reset limit switch in the gas control area. The switch will
open and shut off power to the gas valve if a flame rollout
or overheating condition occurs in the gas control area.
DO NOT bypass the switch. Correct inadequate
combustion-air supply, component failure, or restricted
flue gas passageway before resetting the switch.
II. SEQUENCE OF OPERATION
Using schematic diagram in Fig. 31, follow the sequence of
operation through the different modes. Read and follow diagram
very carefully.
NOTE: If power interruption occurs during "call for heat" (W/W1
or W/W1 and W2), the control will run the blower for the selected
blower off delay period after power is restored, if the thermostat is
TABLE 9A—FURNACE SETUP SWITCH DESCRIPTION
SETUP
SWITCH
NO.
SW-1
SW-2
SW-3
TABLE 9B—BLOWER OFF DELAY SETUP SWITCH (SW)
2–STAGE UNITS WITH PSC BLOWER MOTORS
DESIRED HEATING MODE
BLOWER-OFF DELAY (SEC)
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still calling for gas heating. The amber LED will flash code 12
during this period, after which the LED will be ON continuous as
long as no faults are detected. After this period, the furnace will
respond to the thermostat normally.
The blower door must be installed for power to be conducted
through blower door interlock switch ILK to furnace control CPU,
transformer TRAN, inducer motor IDM, blower motor BLWM,
hot surface igniter HSI, and gas valve GV.
A. Two-Stage Heating With Single-Stage Thermostat
(Adaptive Mode)
(See Fig. 27 for thermostat connections.)
NOTE: Low-heat-only switch, SW-1, selects either the low-heat-
only operation mode when ON, or adaptive heating mode when
OFF, in response to a call for heat. (See Fig. 32.)
This furnace can operate as a 2-stage furnace with a single-stage
thermostat because furnace control CPU includes a programmed
adaptive sequence of controlled operation, which selects low-gas-
heat or high-gas-heat operation. This selection is based upon the
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stored history of the length of previous gas heating on/off periods
of the single-stage thermostat.
The furnace will start up in either low- or high-gas heat. If the
furnace starts up in low-gas heat, the control CPU determines the
low-gas heat on time (from 0 to 16 minutes) which is permitted
before switching to high-heat.
If power is interrupted, the stored history is erased. When this
happens, the control CPU will initially select low-heat for up to 16
minutes and then switch to high-heat, as long as the thermostat
continues to call for heat. Subsequent selection is based on stored
history of thermostat cycle times.
When wall thermostat "calls for heat", R-W/W1 circuit closes. The
furnace control performs a self check, verifies the low-heat and
high-heat pressure switch contacts LPS and HPS are open, and
starts inducer motor IDM in high speed.
1. Inducer Prepurge Period- If the furnace control CPU
selects low-heat operation the inducer motor IDM comes up
to speed, the low-heat pressure switch LPS closes, and the
—34—
SWITCH NORMAL
NAME POSITION
Allows 2-stage operation with a
single-stage thermostat when
connected between R to W2.
Adaptive
Turn on when using 2-stage
Heat OFF
thermostat to allow Low Heat
Mode
operation when R to W/W1 closes
and High Heat operation when
R to W/W1 and W2 close.
Control blower OFF
Blower
OFF ON or OFF
conjunction with SW-3.
delay
Control blower OFF
Blower
OFF ON or OFF
conjunction with SW-2.
delay
90
120
150
180
DESCRIPTION
OF
USE
delay time. Used in
See Table 9B.
delay time. Used in
See Table 9B.
SETUP SWITCH
SW-2 SW-3
OFF OFF
OFF ON
ON OFF
ON ON