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V. FURNACE SECTION CONTROLS AND IGNITION
V. SYSTEM
NORMAL FURNACE OPERATING SEQUENCE
This unit is equipped with a two stage integrated direct spark ignition control.
NORMAL HEAT MODE
A. Call For First Stage (low fire) Only:
1. Zone thermostat contacts close, a call for first stage (low fire) heat is initiated.
2. Control runs self check.
3
. Control checks the high-limit switch for normally closed contacts, each pressure switch
for normally open contacts, and all flame rollout switches for continuity.
4. Control energizes each low-fire inducer.
5. Control checks each low-fire pressure switch for closure.
6. If each low-fire pressure switch is closed, the control starts a 30 second prepurge. If
either low-fire pressure switch is still open after 180 seconds, the high-fire inducers will
be energized until closure.
7. After prepurge timeout, control initiates spark for 2 seconds minimum, 7 second maxi-
mum ignition trial, initiates 45 second, second stage (high fire) warm up timing.
8. Control detects flame, de-energizes spark and initiates 45 second delay on blower tim-
ing.
9. After a fixed 45 seconds indoor blower delay on, the control energizes the indoor blow-
er.
10. After the 45 second second stage warmup period control checks thermostat input. If
only W1 is called for, W2 is de-energized and the control starts a 5 second off delay on
the W2 inducer.
11. After fixed 5 seconds the W2 inducer is de-energized.
12. Control enters normal operating loop where all inputs are continuously checked.
B. Call For Second Stage, After First
Stage Established; Starting from A.11:
1. If a call for second stage (high fire) is initiated after a call for first stage heat is estab-
lished, the control energizes the W2 inducer assures the high-fire pressure switch is
closed and energizes the second stage of the gas valve.
2. Control enters normal operating loop where all inputs are continuously checked.
C. Second Stage Satisfied; First Stage
Still Called For; Starting From B.2:
1. Once the call for second stage is satisfied, the control starts a 30 second off delay on
W2 inducer and reduces the gas valve to first stage.
2. Control enters normal operating loop where all inputs are continuously checked.
D. First Stage Satisfied:
1. Zone thermostat is satisfied.
2. Control de-energizes gas valve.
3. Control senses loss of flame.
4. Control initiates 5 second inducer postpurge and 90 second indoor blower delay off.
5. Control de-energizes inducer blower.
6. Control de-energizes indoor blower.
7. Control in the stand by mode with solid red LED.
E. First Stage and Second Stage Called
Simultaneously:
1. Zone thermostat contacts close, a call for first stage (low fire) and second stage (high
fire) heat is initiated.
2. Control runs self check.
3. Control checks the high-limit switch for normally closed contacts, each pressure switch
for normally open contacts, and all flame rollout switches for continuity.
4. Control energizes each low-fire inducer.
5. Control checks each pressure switch for closure.
6. If each low-fire pressure switch is closed, the control starts a 30 second prepurge. If
either switch is still open after 180 seconds, the high-fire inducers will be energized
until closure.
7. After prepurge timeout, control initiates spark for 2 seconds minimum, 7 second maxi-
mum ignition trial, and initiates 45 second second stage warm up timing.
8. Control detects flame, de-energizes spark and starts a 45 second indoor blower delay
on timing.
9. After a fixed 45 seconds indoor blower delay on, the control energizes the indoor blow-
er.
10. After the 45 seconds second stage warmup period control checks the thermostat input.
If W1 and W2 is present control enters normal operating loop where all inputs are con-
tinuously checked.
F. First Stage and Second Stage
Removed Simultaneously:
1. Upon a loss of W1 and W2 the gas valve is de-energized.
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