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
Integrated Controls with Hot Surface
Ignition.
1. Each time the thermostat “W”
(Heating) contacts close, the
induced draft blower (inducer)
begins a prepurge cycle.
2. The air proving negative pressure
switch(es) closes.
3.
5 seconds after the pressure
switch(es) close, the hot surface
igniter begins heating for 30
seconds
to full temperature. The
induced draft blower operates for the
complete heating cycle.
4. After the 30-second igniter warm up,
the gas valve opens for an
8-second trial for ignition.
5. The igniter lights the gas burners
and
stays energized for the first 7
seconds after the gas valve
opens.
6. 8 seconds after the gas valve opens
the remote 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
approximately 20 seconds after the
burners ignite.
8. When the thermostat “W” (Heat Call)
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 35 seconds to
prepurge.
2. 5 seconds into prepurge, the hot
surface igniter heats for 30 seconds.
The inducer continues to run.
3. After the 30-second igniter warm up,
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 during the 8th
second after the gas valve opens,
the gas valve closes, and the igniter
de-energizes.
5. After 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 30-second pre-
purge, the igniter energizes and
begins a 30-second warm-up period
(inducer is still running). After a 30-
second igniter warm-up period (60
sec. of ind. running), the gas valve
opens and the control looks for a
flame signal for up to 8 seconds. If
no flame is sensed, the control goes
into “self-healing” mode, in which the
blower and inducer both run for three
minutes before another ignition
attempt is made.
NOTE: The following applies only
to units manufactured before third
Quarter 2003:
After 5-second inter-
purge, the control begins a 30-
second pre-purge followed by a 30-
second igniter warm-up period
(inducer is still running). After the 30-
second igniter warm-up period, the
gas valve opens and the control
looks for a flame signal for up to 8
seconds. If no flame is sensed, the
control goes into “self-healing”
mode, in which the blower and
inducer both run for three minutes
before another ignition attempt is
made.
6. The control attempts to ignite up to
four times (first attempt followed by
three retries). After the fourth
failure to ignite, the control goes
into a one-hour “soft-lockout,”
during which the control will not
respond to the thermostat heat call
(W). The lockout can be reset by
shutting off main power to the
furnace for five seconds, or by
turning the heat call (W) from the
thermostat off and then back on.
Note that second and fourth
ignition attempts will have a 30-
second pre-purge followed by a 30-
second igniter warm-up period.
This prevents the igniter from
overheating.
7. The above sequence will repeat
after a one hour delay. It will
continue repeating until ignition is
successful or the call for heat is
terminated.
8.
To reset the lock out, make and
break power either at the
thermostat or at the unit
disconnect switch for 5 to 10
seconds.
It then goes through
another set of trials for ignition.
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.
!
WARNING
46
