LIAF300
Twinning Connection
When the twin terminals of 2 controls are wired together, the controls will operate their heat blowers at the same time. Connecting a G call on one control will immediately activate the heat
blower on both controls. Removing the G call will immediately deactivate the heat blower on both controls. When the heat blower turns on during the heat cycle of one unit, the heat blower of
the second unit turns on at the same time.
Twinning Error
A twin communication fault is detected if the 24 VAC supplies to the twins are not in phase with each other, or power is removed from one of the twins. While a Twin Fault exists, the control
does not respond to thermostat commands and flashes “5” on the status LED. If a twin fault occurs during a heat cycle, both furnaces terminate the call for heat immediately. If a twin fault
occurs during high speed fan or continuous fan, both controls shut blowers off immediately.
Wiring Diagram
24V SEC
PRI
Blower
Chassis
Ground
Heating
Speed
CAP
IDM
C
L1
L2
115 V
AC
9-Pin Harness Connector
1 N/C
2 Gas valve 24 VAC COM
3 Limit switch IN
4 Gas valve OUT
5 Pressure switch IN
6 Pressure switch OUT
7 Flame sensor
8 Limit switch OUT
9 Flame sensor/chassis ground (24 VAC Common)
Limit
Switches
(N.C.)
Rollout
Switches
(N.C.)
Rollout
Switches
(N.C.)
33
LIM
IN
8
LIM
OUT
5
PS
IN
6
PS
OUT
2
GV
COM
4
GV
OUT
7
FS
9
GND
NO
C
Gas Valve
(N.O.)
Flame
Sensor
Probe
N.C.
LEGEND
N.C. Normally Closed
N.O. Normally Open
N/C No Connection
PS Pressure Switch
GND Earth Ground
IDM Inducer Draft Motor
PRI Primary
SEC Secondary
L1 Line 1 (115 VAC)
L2 Line 2 Neutral
CAP Capacitor
GV Gas Valve
FS Flame Sensor
LIM Limit Switch
Spark Electrode
Earth
Ground
Fault Codes, Status Lights and Troubleshooting
Flashes
Fault Condition
Trouble Shooting
Solid On
Normal operation
Normal operation
Solid Off
Gas valve fault
Check gas supply to the furnace is turned on. Check for proper voltage to the gas valve during the cycle, check for shorted or
miswired gas valve, and check harness for any shorts or breaks in the wires.
1
Pressure switch stays open continuously
Check for obstructed pressure switch tubing or defective pressure switch. Check for oxidation on terminals, broken wires, or
defective inducer motor . Check for proper voltage at the inducer motor input.
2
Pressure stays in closed position continu-
ously
Check to see if inducer is constantly running and keeping pressure switch closed, check if voltage is being inadvertently applied
to the pressure switch when it should not be, and check or replace pressure switch.
3
Open Limit switch
Check for blocked airflow, blocked ductwork, defective rollout switches
4
Ignition failure Lockout
The number of retry’ s or recycles has exceeded the limit for the control. Clean or replace the flame sensor, check the spark
igniter for proper operation and grounding, and check the transformer’s common is grounded to earthground.
5
Twining fault
Ensure the commons of both furnace’s transformers are tied together and tied to earth ground. Check the wire between the twin
terminals of each furnace is good, clean,& tight. Check that each furnace is earth grounded. If twinning persists, reverse the
polarity of the secondary wires on the step-down transformer (SEC and COM at the transformer 24 VAC).
6
Limit Switch Lockout
Max number of trials for open limit switch reached and unit is in a safety lockout. Check the high temperature limit switch and
rollout switches with a multimeter for proper operation and check the wiring attached to the limit switch circuit for any breaks or
oxidation of terminals. Check for any airflow obstructions. Replace limit switch or rollout switches if defective.
7
Flame loss lockout
Maximum number of trials for flame establishment reached, unit in lockout due to no flame sensed. Clean or replace flame
sensor assembly and check the earth ground to the furnace.
**Note:
Gas valve fault lockout –
If the control senses voltage across the gas valve terminals when it is supposed to be deactivated, the control goes into lockout. The status LED
turns off, and the inducer comes on after 15s. If the gas valve fault is cleared, the inducer will turn off immediately, but the status LED will stay off and the control remains in lockout.
The gas valve lockout cannot be cleared by toggling a W call; the control must be power cycled, or wait 1 hour after the gas valve fault clears.
