WARNING: Troubleshooting of components necessarily re-
quires opening the electrical control box with the
power connected to the unit. Use extreme care
when working with live circuits! Check the unit
nameplate for the correct line voltage and set the
volt meter to the correct range before making any
connections with line terminals.
WARNING: Prior to any of the following maintenance proce-
dures, shut off all electric power to the unit to
prevent personal injury.
CAUTION: Label all wires prior to disconnection when servic-
ing controls. Wiring errors can cause improper and
dangerous operation. Verify proper operation after
servicing.
NOTE: To find the Btu input, multiply the number of cubic feet of
gas consumed per hour by the Btu content of the gas in
your particular locality (contact your gas company for this
information - it varies widely from city to city.)
1. The indoor blower motor is a non-inherently protected
three-phase motor. Protection is provided by an overload
relay for overcurrent and fuses for short circuit. If the motor
fails to run, check the line voltage circuit and control voltage
circuit per the following procedure:
a. If the Indoor Blower Motor does not operate, check
visually that contactor 3M is pulled in. If so, check for
line voltage between all three phases at the line termi-
nals of the Blower Overload Relay (BOR). If line voltage
is found, check the leads to the blower motor for open
circuit. If line voltage is found at the motor leads (inside
the conduit box on the motor shell), disconnect the
motor and check for open windings per the motor wiring
diagram. If open windings are found, replace the motor.
If line voltage is not found at the BOR, trace the leads
back to the field supply terminal block, checking for an
open circuit or blown fuses.
b. If the contactor 3M is not pulled in, check for control
voltage (24V) at the 3M coil. If voltage is found, replace
the contactor. If control voltage is not found at 3M, check
for voltage across terminals 95 & 96 of the BOR. If
voltage exists, the BOR is open on overload. The BOR
should be set to the auto reset position. The BOR must
cool down in order to reset. If the BOR will not reset,
replace the BOR. If the BOR resets and 3M pulls in, but
the indoor blower motor will still not run, refer to para.
(a) for troubleshooting the line voltage supply circuit. If
control voltage is not found at the BOR, trace the circuit
back to the relay board and thermostat per the unit
wiring diagram. Replace any defective components.
2. Draft motor operates and furnace lights but supply air
blower does not start after a short time delay with room
thermostat fan switch set to “AUTO”.
a. Set fan switch to “ON”. If blower motor runs, go to Step f.
If it does not, check to see if line voltage is being
supplied to the contacts of the contactor (3M), and if the
contactor is pulled in. Check for loose wiring.
b. If contactor (3M) is pulled in, proceed with the trou-
bleshooting steps indicated in Step 1 above.
c. If (3M) is pulled in and the blower motor still does not
run, replace the blower motor.
d. If (3M) is not pulled in, check for 24 volts at the (3M)
coil. If 24 volts is present, replace the (3M) contactor.
e. If 24 volts is not present at the (3M) coil, check for loose
24 volt wiring back to the relay board. Check control
wiring to the room thermostat. If all is fine, replace the
relay board.
f. If the blower motor runs with the fan switch in the “ON”
position but does not run soon after the furnace has
ignited with the fan switch in the “AUTO” position, check
for loose 24 volt wiring between the relay board in the
main control box, the Mate-N-Lok connector in the
partition between the evaporator and gas heat sections
and the time delay relay (TDR).
g. If all control wiring is fine, check for 24 volts at the relay
board. If 24 volts is present, replace the relay board. If
24 volts is not present, replace the (TDR) relay.
NOTE: The furnace may shut itself down on a high tempera-
ture condition during the procedure, but this will not
effect the test if it is done within 5 minutes of furnace
shut-down.
3. 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 heat relay (RW1) contacts in the main control box
and check to see if the (RW1) is pulled in.
d. If the (RW1) relay is pulled in, check for a loose line
voltage connection.
e. If the (RW1) relay is not pulled in, check for 24 volts at
the (RW1) coil. If 24 volts is present, replace the (RW1)
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.
4. The draft motor runs but the furnace does not light and the
sparker does not spark.
a. The ignition control (IC1, IC2) may be locked out due to
either a flame roll out or 100% shut off. These safety
features are described above. If lock-out has occurred,
24V must be removed from the ignition controls. This is
done at the unit or by resetting the room thermostat.
After resetting 24V, check for proper furnace operation.
TROUBLESHOOTING
Cont’d.
530.18-N11Y
Unitary Products Group
21
