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d. Limit over- -temperature switch
e. Gas valve
f. Hot surface ignitor
g. Flame- -sensing electrode
h. DSS Draft Safeguard
14. Reinstall vent connector on furnace vent elbow. Securely
fasten vent connector to vent elbow with two (2)
field- -supplied, corrosion- -resistant, sheet metal screws
located 180_ apart.
15. Replace blower access door only, if it was removed.
16. Set thermostat above room temperature and check furnace
for proper operation.
17. Verify blower airflow and speed changes between heating
and cooling.
18. Check for gas leaks.
19. Replace outer access door.
Representative drawing only, some models may vary in appearance.
Fig. 37 - - Cleaning Heat Exchanger Cell
WARNING
!
FIRE OR EXPLOSION HAZARD
Failure to follow this warning could result in personal injury,
death and/or property damage.
Never purge a gas line into a combustion chamber. Never
test for gas leaks with an open flame. Use a commercially
available soap solution made specifically for the detection of
leaks to check all connections.
SEQUENCE OF OPERATION
NOTE: Furnace control must be grounded for proper operation
of furnace control and flame sensing electrode. Control is
grounded through green/yellow wire routed to gas valve and
burner box screw. Using the schematic diagram in Fig. 38, 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- -second blower- -only ON period two
seconds
after power is restored, if the thermostat is still calling for
gas heating. The LED light will flash 1+2 during the 90- -second
period, after which the LED will flash heartbeat (bright- -dim), as
long as no faults are detected. After the 90- -second blower- -on
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 ignitor HSI, and gas valve GV.
34
Sequence of Operation - - Heating
1. Call for Heat:
The wall thermostat "calls for heat", closing the R
circuit. The furnace control performs a self- -check, verifies
the transducer reads no pressure present, and starts the
inducer motor IDM ramp to prepurge
a. Inducer Prepurge Period: The furnace control CPU
b. Ignitor Warm- -Up: At the end of the prepurge period,
c. Trial for Ignition: When the ignitor warm- -up period is
d. Flame Proving: When the burner flame is proved at the
A190291
e. Blower-On-Delay: If the burner flame is proven a
f. Blower-Off-Delay: When the thermostat is satisfied, the
2. Cooling Mode
The thermostat closes the R
The R
and the R
BLWM at cooling airflow. Cooling airflow (Table 5) is
based on the motor wire lead selection used on the COOL
terminal. The electronic air cleaner terminal EAC- -1 is
energized with 115 vac whenever the blower motor
Specifications are subject to change without notice.
ramps up the inducer motor IDM to prepurge pressure
then the furnace control CPU begins a 15- -second
prepurge period. If the transducer fails to reach target
pressure the inducer motor IDM will remain running until
target pressure is maintained.
the Hot- -Surface Ignitor HSI is energized for a 17- -second
ignitor warm- -up period. Inducer maintains pressure
during ignitor warm- -up.
completed the main gas valve relay contact GVR closes
to energize the gas valve solenoid GV. The gas valve
solenoid GV permits gas flow to the burners where it is
ignited by the HSI. Five seconds after the GVR closes,
a 2- -second flame proving period begins. The HSI ignitor
will remain energized until the flame is sensed or until the
2- -second flame proving period begins.
flame sensor electrode FSE, the inducer motor IDM will
increase speed (after a short delay of 14 seconds on some
models) to a higher RUN pressure. The control will
maintain this pressure once reached, and the furnace
control CPU will begin the blower- -ON delay period
while continuing to hold the gas valve GV open. If the
burner flame is not proved within the 2- -second flame
proving period, the control CPU will open the gas valve
relay GVR, de- -energizing the gas valve solenoid GV.
The control CPU will repeat the ignition sequence for up
to three more Trials- -For- -Ignition before going to an
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 Heating
mode and operate the inducer motor IDM until flame is
no longer proved.
25- -second blower- -ON delay begins from when the gas
valve GV is opened. The blower motor BLWM is turned
ON at heat airflow. Simultaneously, the humidifier
terminal HUM and electronic air cleaner terminal EAC- -1
are energized and remain energized throughout the
heating cycle.
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- -second post- -purge period.
The blower motor BLWM and air cleaner terminal
EAC- -1 will remain energized at heat airflow for 90, 120,
150, or 180 seconds (depending on selection at
blower- -OFF delay switches). The furnace control CPU
is factory- -set for a 120- -second blower- -OFF delay.
-
G and
Y circuit starts the outdoor unit on cooling speed,
-
-
G and
-
Y circuit starts the furnace blower motor
W
-
-
Y circuit for cooling.
441 01 1501 04
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