4
Unitary Products Group
4. Fan Switch -- This fan switch is
a temperature sensing device
that turns on the blower when suf-
ficient heat has built up within the
furnace. It also turns the blower
off when the furnace has cooled
down sufficiently after burner
shut--off. In warm weather, there
is a possibility of the blower com-
ing on periodically or operating
continuously due to a heat build-
up within the furnace by a com-
bination of warm weather and
heat from the pilot. This is normal
operation as long as there is pow-
er to the furnace and the ON--
OFF--FAN switch is at the “ON”
position. IF blower operation is
not desired, the ON--OFF--FAN
switch may be set in the “OFF”
position to cut the electrical pow-
er to the furnace.
INSTRUCTIONS FOR DGAM, DGAT & DLAS AUTOMATIC IGNITION MODELS
LIGHTING INSTRUCTIONS
1. STOP! Read the SAFETY IN
Ć
FORMATION.
2. Set the thermostat to the lowest
setting, or OFF.
3. Turn off all electric power to the
furnace.
4. This appliance does not have a
pilot. It is equipped with an igni-
tion device which automatically
lights the burner. Do not try to
light the burner by hand.
5. Remove upper door panel.
6. Move gas valve control lever to
OFF. See Figure 3.
7. Wait five (5) minutes to clear out
any gas. Then smell for gas, in-
cluding near the floor. If you smell
gas, STOP! Follow “C”, in the
SAFETY INFORMATION. If you
don’t smell gas, go to the next
step.
8. Move gas control control lever to
ON.
9. Replace upper door panel.
10. Turn on all electric power to the
furnace.
11. Set thermostat to desired setting.
GAS CONTROL
CONTROL LEVER
FIGURE 3 -- WHITE--ROGERS
GAS VALVE
PRESSURE
REGULATING
DEVICE
SEQUENCE OF OPERATION
This furnace is equipped with an elec-
tronic control system which automati-
cally supervises burner and fan op-
eration. A green indicator light dis-
plays during normal operation. This
indicator light also informs the home
owner when certain basic services
are needed. In response to a call for
heat by the room thermostat, the
burner is lighted by a hot glowing igni-
tor at the beginning of each operation
cycle. The burner will continue to op-
erate until the thermostat is satisfied
at which time all burner flame is extin-
guished. During the off cycle no gas is
consumed. With the room thermostat
set below room temperature, and with
the electrical power and gas supply to
the furnace on, the normal sequence
of operation is as follows:
1. When the room temperature falls
below the setting of the room
thermostat, the thermostat ener-
gizes the furnace control board.
2. When the furnace control board
is activated, the combustion air
blower is turned on.
3. As the combustion air blower in-
creases in speed, the contacts of
the pressure switch will close and
complete the electrical circuit to
the ignition circuit.
4. During the next 40 to 50 seconds,
the combustion air blower will
bring fresh air into the heat ex-
changer and the ignitor will begin
to glow. At the end of this period,
the gas valve will open and the
burner will light.
5. After the burner lights, a separate
sensor acts as a flame probe to
check for the presence of flame.
As long as flame is present, the
system will monitor it and hold the
gas valve open.
6. If the burner fails to light within
6--8 seconds after the gas valve
opens, the gas valve will close
and the ignitor will be turned off.
After a short pause, the system
will recycle and try again for igni-
tion. If the burner fails to light after
three tries, the ignition system will
lock out. The system will remain
in lock--out mode for a period of
one hour, then the furnace will try
for ignition again.
7. The lapsed time from the moment
the room thermostat closes to
when the burner lights may be
45--60 seconds. This delay is
caused by
a. The time required for the igni-
tor to heat up and
b. The time required for fresh air
to be brought into the heat
exchanger.
8. Approximately 90 seconds after
the burner lights, furnace air cir-
culation blower will run.
9. When room thermostat is satis-
fied, the circuit to the furnace con-
trol board is opened. The circuit
to the combustion air blower and
the gas valve is opened and the
burner is extinguished. Then the
furnace control board will keep
the circulating blower running for
a fixed period of time to allow ad-
ditional heat to be drawn from the
heat exchanger.
10. Diagnostic Light
If furnace does not maintain home
temperature as set, check the light in-
dicator, located behind the upper front
door of the furnace.
