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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
or control will lock out. Control is grounded through
green/yellow wire routed to gas valve and gas valve mounting
bracket screw.
Follow the sequence of operation through the different modes.
Read and follow the wiring diagram very carefully.
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.
Sequence of Operation - - Heating
1. Call for Heat
A call for heat is intiated when a connection is observed
between thermostat terminals "R" & "W".
a. Pressure Sensor Verification:The control operates the
inducer in a manner to verify the pressure sensor null
value and span operation are within specification. If the
system is operating correctly, this test takes only a few
seconds. If the system is not functioning properly, the
control times out after a maximum 90 seconds and
displays the proper fault code.
b. Pre-purge: The heating cycle begins with operation of
the inducer at "Pre-purge" setting for the 30 seconds.
c. Ignitor Warm-Up: After the pre-purge timer expires,
the control will set the inducer to the "Ignitor Warm-Up"
setting and energize the ignitor for the Ignitor Warm-up
period of 17 seconds.
NOTE: Inducer motor shuts off during ignitor warm up period
and then come back on for the ignition trial.
d. Trial for Ignition: Once the ignitor warm-up period has
expired, the control sets the inducer to the "Trial for
Ignition" setting and stabilizes the inducer speed to meet
the target pressure. The gas valve is then energized
allowing the flow of gas to the burner. The gas valve
remains open for the Trial for Ignition interval.
e. Flame Sense: While the gas valve is open, the control
monitors the flame sense circuit to detect the presence of
flame. If flame is not established during the Trial for
Ignition period of 4 seconds, the control de-energizes the
gas valve and operates the inducer for the Inter-purge
period.
f. Flame Stabilization: Once flame is established, the
control will set the inducer to the "Flame Stabilization"
setting and maintain the inducer operation at this setting
for the duration of the Flame Stabilization timing of 10
seconds.
g. Blower On-Delay: Once a successful ignition occurs,
the control will wait for the Heat Blower On-Delay of 25
seconds (time begins when the gas valve is energized) and
then energize the blower heating speed.
h. Heating Cycle Run: After the Flame Stabilization
A190291
period is completed, the control will continue to maintain
the heating cycle with the inducer running at the "Run"
setting until one of the following occurs:
(1.) The call for heat is satisfied (the connection between
(2.) Flame sense is lost (flame out), in which case the
(3.) A lockout condition exists, in which case the control
i. Post-purge: Once the burner cycle has terminated and
loss of flame is verified, the control energizes the inducer
at the "Post-purge" setting for 30s.
j. Inter-purge: In the event of a failed trial for ignition, the
control energizes the inducer at the "Post-purge" setting
for the Inter-purge Timing 45s.
k. Blower Off-Delay:
de-energized, the control continues to operate the blower
on the HEAT speed for the duration of the Heat Blower
Off-Delay timing. The Heat Blower Off-Delay is
field-selectable (90, *120, 150, 180).
NOTE: *120 is default setting.
OFF: The controls returns to the stand- -by mode until either a
thermostat call is received or an error condition occurs.
Sequence of Operation - - Cooling
1. Call for Cool
A call for heat is intiated when a connection is observed
between thermostat terminals "R" & "Y".
a. Blower On-Delay: When the call for cool is initiated,
the control will wait for the Cooling Blower On-Delay
timing of 2 seconds, for both jumper settings.
b. Blower Off-Delay: Once the connection between "R"
and "Y" is removed, the control continues to operate the
blower on the COOL speed for the duration of the Cool
Blower Off-Delay timing (fixed 90 seconds).
OFF: The controls returns to the stand- -by mode until either a
thermostat call is received or an error condition occurs.
Sequence of Operation - - Fan Only
1. Operation:
connection is observed between thermostat terminals "R"
& "G". The "G" terminal is ignored when there is either a
call for heat or call for cool. When in the Fan Only Mode,
the blower will be energized to run on Fan speed.
Fault Code Recall
1. Function: When the SW1 button is pressed momentarily,
the control displays the last five (5) fault codes recorded in
non-volatile memory upon demand.
2. Operation:
thermostat satisfied (no call for heat or cool). Depress and
release the SW1 button once (less than 5 seconds); the
34
"R" & "W" is removed).
control will initiate an inter-purge (45s) and recycle.
terminates the heating call and waits for the error
condition to resolve according to the programmed
parameters.
Once the gas valve has been
Fan Only Mode is initiated when a
The control must be powered and the
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