The pressure switch is a normally open switch that monitors
combustion airflow. If there is adequate airflow, the pressure
switch closes. Inadequate airflow resulting from excessive
venting system restriction or a failed combustion blower will
cause the switch to remain open.
The rollout switch(es) are normally closed switch(es) that open
when abnormal temperatures exist in the burner area. This can
be caused by a restricted heat exchanger causing main burner
flame to "roll out" into the vestibule area or burner box.
The rollout switch(es) must be manually reset by pushing the
button on top to restore furnace operation.
Primary Limit Control
This is a normally closed control that opens if abnormally high
circulating air temperatures occur. It is an automatic reset control.
Safety Interlock Switch
When the blower door is removed, the safety interlock switch
breaks the power supply to the burner controls and blower motor.
Blower Control Board
Electrical Shock Hazard
Disconnect power before servicing.
Replace all parts and panels before operating.
Failure to do so can result in death or electrical shock.
The blower control board operates the circulating air blower, the
combustion blower and any accessories connected to it. There is
a fixed blower "off" delay of 90 seconds, which is one-time
adjustable to 150 seconds. See Wiring Connection Diagram.
Gas Control Valve
The gas control valve contains control logic to sense proper
operating conditions and provides gas flow and ignition only
when all conditions are properly met. The gas control valve also
regulates the manifold gas pressure.
Furnace Fails to Operate Properly
Review "Sequence of Operation" and visually inspect the
following before troubleshooting:
Is the power to the furnace on?
Is the blower compartment door securely closed?
Are the manual shutoff valves in the gas line to the furnace open?
The system has a built-in, self-diagnostic capability. The control
continuously monitors its own operation and the operation of the
system. If a system problem occurs, a failure code is indicated by
the LED on the gas control valve. See the Failure Codes chart for
a description of the flash codes.
IMPORTANT: Do not remove the blower compartment door or
turn off the power to the furnace because either action will clear
the control's memory of the failure.
1. Start the system by setting the thermostat above the room
2. Observe the system's response.
3. Use the information provided in this section to check the
No Power to the System Control
Normal Operation (Standby or call for heat)
Pressure switch closed when it should be
Pressure switch stuck open 30 seconds or
longer after call for heat (system in 5-minute
delay mode before next call for heat). On/off
switch in OFF position during a call for heat
will generate this code.
Open Limit Switch or Limit Switch Circuit
Flame Sense Signal sensed out of proper
* 11 or more flashes with no pause