W415-2845 / B / 11.10.20
47
IOM
H3.24
SHOULD OVERHEATING OCCUR OR THE GAS BURNERS FAIL TO SHUT OFF, CLOSE THE
MANUAL GAS VALVE FOR THE FURNACE BEFORE SHUTTING OFF THE ELECTRICAL
POWER TO THE FURNACE. FAILURE TO DO SO CAN CAUSE AN EXPLOSION OR FIRE
RESULTING IN PROPERTY DAMAGE, PERSONAL INJURY OR LOSS OF LIFE.
BEFORE RESTARTING THE FURNACE, CHECK ALL PLASTIC VENTS AND WIRES
FOR DAMAGE.
WARNING
!
!
17.3 SEQUENCE OF OPERATION
1. Room temperature drops causing the room thermostat call
or
rst stage heat by connecting
W1” to
R”.
The control verifi es the limit switch is closed and both low and high pressure switches are open. The
control energizes the exhauster motor on high speed and waits for the low pressure switch to close. The
exhauster remains on high speed and begins a 15 second pre-purge period. The high pressure switch is
ignored. If the low pressure switch does not close within 60 seconds, the control will fl ash “2” on the Red
Status LED, and de-energize the exhauster for 60 minutes.
2. When the 15 second pre-purge time has elapsed, the control energizes the HSI output for a 15 second
warm-up period (15 seconds on retries). The control energizes the low main gas valve. 4 seconds after the
gas is energized, the control de-energizes the HSI output and leaves the gas energized another 1 second
for fl ame proving. If fl ame is present at the end of trial for ignition time, the control leaves the gas valve
energized, exhauster on high speed, and begins heat blower on delay. The control always ignites on high
exhauster/low gas and ignores second stage call for heat until low fi re is established for 15 seconds.
3. Blower on delay time begins when the gas valve is energized. The control provides the motor low heat
speed signal when fl ame is proven, and starts a 30 second blower delay before full capacity blower level.
4. When there is a demand for 2nd stage heat from thermostat W2 or automatic staging, the control changes
the exhauster from low to high speed. When high pressure switch closes, the control changes indoor
blower speed from Low heat to High heat and energizes high gas output. If the high pressure switch is
open the Green LED will fl ash. If the high pressure switch is closed the Green LED will be on. High gas
valve drops out while High pressure switch is open because it is directly in series with the high pressure
switch.
5. When the thermostat W2 call ends and W1 remains (two stage thermostat), the control de-energizes the
high gas output and immediately changes exhauster speed from high to low. With the thermostat heating
contacts open (single stage thermostat), the fl ames extinguish immediately and the exhauster blower
stops after a 5 second post purge time.
6. Blower off delay is handled by the motor. The control de-energizes the motor heat signal when the gas
valve de-energizes, and starts a programmed delay period.
IN THE EVENT OF FLAME FAILURE:
If fl ame is lost, the control de-energizes the gas valve within 2 seconds, switches the exhauster motor to
high speed (if not already on high), and begins timing the inter-purge delay. The indoor blower motor will be
energized and/or remain energized on heat speed for the programmed delay off time. When the inter-purge
delay is over, the control will re-cycle up to 5 fl ame losses (4 re-cycles) within a single call for heat before
going into lockout. The control fl ashes “8” on the Red LED if lockout is due to too many fl ame dropouts (1 hour
lockout).
H21.3.2B
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