50
START-UP PROCEDURES
This furnace is equipped with a direct
ignition device. Each time the room
thermostat calls for heat, the ignitor
lights the main burners directly. See the
lighting instructions on the furnace.
TO START THE FURNACE
1. Remove the burner compartment
control access door.
2.
IMPORTANT:
Be sure that the
manual gas control has been in the
“OFF” position for at least five
minutes. Do not attempt to manually
light the main burners.
3. Turn off the furnace electrical power
and set the room thermostat to its
lowest setting.
4. Turn the gas control knob to the
“ON” position or move the gas
control lever to the “On” position.
5. Replace the burner compartment
control access door.
6. Turn on the furnace electrical power.
7. Set the room thermostat to a point
above room temperature to light the
main burners.
8. After the burners are lit, set the room
thermostat to a desired temperature.
TO SHUT DOWN
THE FURNACE
1. Set the room thermostat to its lowest
setting and wait for furnace to shut
down.
2. Remove the burner compartment
control access door.
3. Shut off the gas to the main burners
by turning the gas control knob to
the “OFF” position. See Figure 37.
SHOULD OVERHEATING OCCUR OR
THE GAS SUPPLY FAIL TO SHUT
OFF, CLOSE THE MANUAL GAS
VALVE FOR THE APPLIANCE
BEFORE SHUTTING OFF THE
ELECTRICAL SUPPLY. FAILURE TO
DO SO CAN CAUSE AN EXPLOSION
OR FIRE RESULTING IN PROPERTY
DAMAGE, PERSONAL INJURY OR
DEATH.
SEQUENCE OF OPERATION
UT ELECTRONIC CONTROLS &
INVESYS CLIMATE CONTROLS
UT Electronic Controls Direct Spark
Ignition
1. Each time the thermostat contacts
close, the induced draft blower
(inducer) begins a prepurge cycle.
2. The air proving negative pressure
switch(es) closes.
3.
30 seconds after the pressure
switch(es) close, the spark igniter
energizes.
The induced draft blower
operates for the complete heating
cycle.
4. After the spark igniter energizes, t
he
gas valve opens for a 8 second
trial for ignition.
5. The igniter lights the gas burners.
6. After the gas valve opens t
he flame
sensor must prove flame ignition
for one second
using the process of
flame rectification. If the burners
don’t light, the system goes through
another ignition sequence. It does
this
up to four
times.
7. The main blower starts 20 seconds
after the burners ignite.
8. When the thermostat cycle ends, the
gas valve closes, the burners go out,
the induced draft blower stops after
a
10-second post-purge,
and the
negative pressure switch(es) open.
9. The main blower continues until
timed off by the setting on the
integrated furnace control board.
Sequence if the system doesn’t
light or doesn’t sense flame:
1. On a call for heat, the control
runs the inducer for 30 seconds
to pre-purge.
2. After the 30-second pre-purge,
the spark igniter energizes. The
inducer continues to run.
3. After the spark igniter energizes,
the gas valve opens for an 8-
second trial for ignition. The
inducer continues and the igniter
stays energized.
4. If flame is not sensed within 8
seconds after the gas valve
opens, the gas valve closes, the
igniter de-energizes and:
5. The inducer completes a 10-
second post-purge, the inducer
stops, and the control verifies that
the pressure switch has opened.
Once the open pressure switch is
confirmed, the control begins the
next ignition cycle by energizing
the inducer for a pre-purge of 30
seconds. After the pre-purge, the
igniter energizes and the gas
valve opens (inducer continues to
run). If no flame is sensed on the
second attempt, the control goes
into a “self-healing” mode, in
which the blower and the inducer
run for 3 minutes before another
ignition attempt is made.
!
WARNING
