2. The supply air blower operates but the draft motor does not
when the room thermostat is set to call for heat and the fan
switch in the “ON” position.
a. The draft motor has inherent protection. If the motor shell
is hot to the touch, wait for the internal overload to reset.
b. If the motor shell is cold with the room thermostat calling
for heat, check for line voltage at the motor’s Mate-N-
Lok connector attached to the evaporator partition. If
line voltage is present, replace the draft motor.
c. If line voltage is not present, check for line voltage at
the draft motor relay “DMR” or “DMC” contacts in the
main control box and check to see if the “DMR” or
“DMC” is pulled in.
d. If the “DMR” or "DMC" relay is pulled in, check for a
loose line voltage connection.
e. If the “DMR” or “DMC” relay is not pulled in, check for
24 volts at the “DMR” or 24 volts at the “TMC-G” terminal
coil. If 24 volts is present, replace the “DMR” or “DM”
relay. If 24 volts is not present, check for a loose 24 volt
connection back to the relay board and check the
connections from the room thermostat to the relay
board. If all connections are correct, replace the relay
board.
3. The draft motor runs but the furnace does not light and the
sparker does not spark.
a. Check all 24 volt connections from the relay board to
and in the gas heat section. Check low voltage connec-
tions to the “BT” and “DMC” or “ETD” located in the
control box.
b. If the furnace is hot, it may be out on an over tempera-
ture condition, wait for limit reset.
c. With the draft motor running, check for 24 volts at
terminal 24V on the ignitor control (IC) where the red
lead from the draft motor attaches. If 24 volts is not
present, the centrifugal switch (CS) has not closed or
has gone bad. Check the line voltage to the unit, if it is
correct replace the draft motor. If line voltage is low call
the power company.
d. If 24 volts is present at the ignitor control, check all
control wiring at the ignitor control and the high tension
wire to the ignitor. Check that the greeen ground wires
from the ignitor control, the gas valve and pilot burner
are all intact and making good electrical connection.
Check to make sure that the ceramic insulator on the
pilot ignitor or sensor is not broken or cracked, if all are
intact replace the ignition control “IC”.
4. The draft motor runs and the sparker sparks at the pilot
burner but the pilot does not ignite and a gas odor is not
detected at the draft motor outlet.
a. Check to make sure gas is being supplied to the unit.
Make sure that the gas pressure to the unit is within the
proper limits as described in the “POST START CHECK
LIST” and that the pilot adjust screw is allowing some
flow of gas as described in “PILOT CHECKOUT”.
b. Check all wiring between the ignitor control and the gas valve.
Check to make sure the ground connections are intact.
c. If the wiring is intact, check for 24 volts across terminals
“PV” and “COMMON” on the ignitor control. If 24 volts
is not present, replace the ignitor control.
d. If 24 volts is present, remove the pilot burner and
remove the pilot orifice from the pilot burner. The orifice
is removed in the direction opposite the flow of gas.
Inspect the orifice for obstruction. If it is clear, replace
the main gas valve.
5. The sparker sparks at the pilot burner but the pilot does not
ignite and a gas odor is detected at the draft motor outlet.
a. Adjust the pilot adjust screw on the gas valve as de-
scribed in “PILOT CHECKOUT”.
b. Check the supply pressure as described in “POST
START CHECK LIST”. Make adjustments as necessary.
c. Check the pilot orifice for obstruction as described in
Item 4. Clean as needed but the problem should not be
the gas valve.
6. The pilot burner ignites but the sparker continues to spark
and the main burners do not ignite.
a. Make the same checks and adjustment as described in Item 5.
b. Make sure that the pilot burner is not bent or damaged.
c. Make sure that the ground connections at the pilot
burner, gas valve and ignitor control are intact. Check
the high tension wire for good electrical connection. If
all are intact, replace the ignitor module.
7. The pilot burner lights and the spark stops but the main
burners do not light.
a. Check electrical connections between the ignitor con-
trol and the gas valve. If intact, check for 24 volts across
terminals “MV” and “COMMON” terminals. If not voltage
detected, replace ignitor control If voltage is present,
replace gas valve.
8. Furnace lights with roll out or one burner has delayed ignition.
a. Make sure that the pilot burner is aligned properly with
the carryover as described in “PILOT CHECKOUT”.
b. Make sure that the carryovers on adjoining burners are
screwed fast and are level with respect to one another.
9. Main burners light but exhibit erratic flame characteristics.
a. Adjust air shutters as described in “BURNER AIR
SHUTTER ADJUSTMENT”.
b. Check the main burner orifices for obstruction and
alignment. Removal procedure is described in
“BURNER INSTRUCTIONS”. Clean or replace burner
orifices and burners as needed.
530.18-N8W
Unitary Products Group
19
