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926SA: Installation, Start-up, Operating, Service and Maintenance Instructions
SEQUENCE OF OPERATION
NOTE: Furnace control must be grounded for proper operation or
control will lock out. Control is grounded through green/yellow wire
routed to gas valve and manifold bracket screw. Using the schematic
diagram in
Fig.
74, follow the sequence of operation through the
different modes. Read and follow the wiring diagram very carefully.
NOTE: If a power interruption occurs during a call for heat (W), the
control will start a 90-sec blower-only ON period two sec after power is
restored, if the thermostat is still calling for gas heating. The Amber
LED light will flash code 12 during the 90-sec period, after which the
LED will be ON continuous, as long as no faults are detected. After the
90-sec period, the furnace will respond to the thermostat normally.
The blower door must be installed for power to be conducted through the
blower door interlock switch ILK to the furnace control CPU,
transformer TRAN, inducer motor IDM, blower motor BLWM,
hot-surface igniter HSI, and gas valve GV.
1. Heating
See
Fig. 39
and
Fig. 40
for thermostat connections.
The wall thermostat "calls for heat," closing the R-to-W circuit.
The furnace control performs a self-check, verifies the pressure
switch contacts LPS and HPS are open, and starts the inducer motor
IDM.
a. Inducer Prepurge Period- As the inducer motor IDM comes up
to speed, the collector box pressure switch contacts LPS close to
begin a 15-sec prepurge period. The inducer housing pressure
switch contacts HPS are ignored until one minute after the gas
valve closes.
b. Igniter Warm-Up- At the end of the prepurge period, the
Hot-Surface igniter HSI is energized for a 17-sec igniter
warm-up period.
c. 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, and 24 vac power
is supplied for a field-installed humidifier at the HUM terminal.
The gas valve GV permits gas flow to the burners where it is
ignited by the HSI. Five sec after the GVR closes, a 2-sec flame
proving period begins. The HSI igniter will remain energized
until the flame is sensed or until the 2-sec flame proving period
begins.
d. Flame-Proving- When the burner flame is proved at the
flame-proving sensor electrode FSE, the furnace control CPU
begins the blower-ON delay period and continues to hold the gas
valve GV open. If the burner flame is not proved within two sec,
the control CPU will close the gas valve GV, and the 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 or 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, 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 until flame is no longer proved.
e. Blower-On Delay- If the burner flame is proven, the blower
motor is energized on HEAT speed 25 sec after the gas valve GV
is energized.
Simultaneously, the electronic air cleaner terminal EAC-1 is
energized and remains energized as long as the blower motor
BLWM is energized.
f. Blower-Off Delay- When the thermostat is satisfied, the R-to-W
circuit is opened, de-energizing the gas valve GV, stopping gas
flow to the burners, and de-energizing the humidifier terminal
HUM. The inducer motor IDM will remain energized for a
15-sec post-purge period. The blower motor BLWM and air
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
cleaner terminal EAC-1 will remain energized for 90, 120, 150,
or 180 sec (depending on the blower-OFF delay selection). The
furnace control CPU is factory-set for a 120-sec Blower-OFF
delay.
2. Cooling mode
The thermostat "calls for cooling".
a. Single-Speed Cooling-
See
Fig. 39
and
Fig. 40
The thermostat closes the R-to-G-and-Y circuits. The R-to- Y
circuit starts the outdoor unit, and the R-to-G-and-Y/Y2 circuits
start the furnace blower motor BLWM on cooling airflow.
Cooling airflow is based on the A/C selection shown in
The electronic air cleaner terminal EAC-1 is energized with 115
vac when the blower motor BLWM is operating.
When the thermostat is satisfied, the R-to-G-and-Y circuits are
opened. The outdoor unit will stop, and the furnace blower motor
BLWM will continue operating at cooling airflow for an
additional 90 seconds. Jumper Y/Y2 to DHUM to reduce the
cooling off-delay to 5 seconds. See
b. Single-Stage Thermostat and Two-Speed Cooling (Adaptive
Mode) -
See
Fig. 39
and
Fig. 40
This furnace can operate a two-speed cooling unit with a
single-stage thermostat because the furnace control CPU
includes a programmed adaptive sequence of controlled
operation, which selects low-cooling or high-cooling operation.
This selection is based upon the stored history of the length of
previous cooling period of the single-stage thermostat.
NOTE: The air conditioning relay disable jumper ACRDJ must be
connected to enable the adaptive cooling mode in response to a call for
cooling. See
Fig.
39. When ACRDJ is in place the furnace control CPU
can turn on the air conditioning relay ACR to energize the Y/Y2 terminal
and switch the outdoor unit to high-cooling.
The furnace control CPU can start up the cooling unit in either low- or
high-cooling. If starting up in low-cooling, the furnace control CPU
determines the low-cooling on-time (from 0 to 20 minutes) which is
permitted before switching to high-cooling. If the power is interrupted,
the stored history is erased and the furnace control CPU will select
low-cooling for up to 20 minutes and then energize the air conditioning
relay ACR to energize the Y/Y2 terminal and switch the outdoor unit to
high-cooling, as long as the thermostat continues to call for cooling.
Subsequent selection is based on stored history of the thermostat cycle
times.
The wall thermostat "calls for cooling", closing the R-to-G-and-Y
circuits. The R-to-Y1 circuit starts the outdoor unit on low-cooling
speed, and the R-to-G-and-Y1 circuits starts the furnace blower motor
BLWM at low-cooling airflow which is the true on-board CF selection
as shown in
Fig.
61.
If the furnace control CPU switches from low-cooling to high-cooling,
the furnace control CPU will energize the air conditioning relay ACR.
When the air conditioning relay ACR is energized the R-to-Y1 and -Y2
circuits switch the outdoor unit to high-cooling speed, and the
R-to-G-and-Y1 and Y/Y2 circuits transition the furnace blower motor
BLWM to high-cooling airflow. High-cooling airflow is based on the
A/C selection shown in
Fig.
NOTE: When transitioning from low-cooling to high-cooling the
outdoor unit compressor will shut down for 1 minute while the furnace
blower motor BLWM transitions to run at high-cooling airflow.
The electronic air cleaner terminal EAC-1 is energized with 115 vac
whenever the blower motor BLWM is operating.
When the thermostat is satisfied, the R-to-G-and-Y circuit are opened.
The outdoor unit stops, and the furnace blower BLWM and electronic air
cleaner terminal EAC-1 will remain energized for an additional 90
seconds. Jumper Y/Y1 to DHUM to reduce the cooling off-delay to 5
seconds. See
Fig.
39.
71
for thermostat connections
Fig.
39.
for thermostat connections.
39.
Fig.
61.
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