A number of safety circuits are employed to ensure safe and
proper furnace operation. These circuits serve to control any
potential safety hazards and serve as inputs in the monitoring
and diagnosis of abnormal function. These circuits are con-
tinuously monitored during furnace operation by the integrated
The integrated control module is an electronic device which
controls all furnace operations. Responding to the thermostat,
the module initiates and controls normal furnace operation, and
monitors and addresses all safety circuits. If a potential safety
concern is detected, the module will take the necessary pre-
cautions and provide diagnostic information through an LED.
The primary limit control is located on the partition panel and
monitors heat exchanger compartment temperatures. It is an
automatic reset, temperature sensor. The limit guards against
the overheating resulting from insufficient air passing over the
The auxiliary limit control is located either on or near the circu-
lator blower and monitors heat exchanger compartment tem-
peratures. The control is an automatic reset, temperature
sensor. It guards against overheating resulting from insufficient
air passing over the heat exchanger.
The rollout limit controls are mounted on the burner/manifold
assembly and monitor the burner flame. They are manual-
reset, temperature sensors. This limit guards against burner
flames not being properly drawn into the heat exchanger.
The pressure switches are normally-open, negative air pres-
sure-activated switches. They monitor the airflow (combustion
air and flue products) through the heat exchanger via pressure
taps located on the induced draft blower. These switches guard
against insufficient airflow (combustion air and flue products)
through the heat exchanger.
The flame sensor is a probe mounted to the burner/manifold
assembly which uses the principle of flame rectification to de-
termine the presence or absence of flame.
NOTE: Discharge body's static electricity before touching unit.
An electrostatic discharge can adversely affect electrical
Use the following precautions during furnace installation and
servicing to protect the integrated control module from dam-
age. By putting the furnace, the control, and the person at the
same electrostatic potential, these steps will help avoid expos-
ing the integrated control module to electrostatic discharge.
This procedure is applicable to both installed and uninstalled
1. Disconnect all power to the furnace. Do not touch the
integrated control module or any wire connected to the
control prior to discharging your body's electrostatic
charge to ground.
2. Firmly touch a clean, unpainted, metal surface of the
furnace away from the control. Any tools held in a
person's hand during grounding will be discharged.
3. Service integrated control module or connecting wiring
following the discharge process in step 2. Use caution
not to recharge your body with static electricity; (i.e., do
not move or shuffle your feet, do not touch ungrounded
objects, etc.). If you come in contact with an ungrounded
object, repeat step 2 before touching control or wires.
4. Discharge your body to ground before removing a new
control from its container. Follow steps 1 through 3 if
installing the control on a furnace. Return any old or
new controls to their containers before touching any
Refer to the troubleshooting chart in the Appendix for assis-
tance in determining the source of unit operational problems.
The red diagnostic LED blinks to assist in troubleshooting the
unit. The number of blinks refer to a specific code.
NOTE: To clear all alarm codes, depress the push button for 6
The ignition control is equipped with a momentary push button
switch that can be used to display on the diagnostic LED the
last five faults detected by the control. The control must be in
Standby Mode (no thermostat inputs) to use the feature. De-
press the pushbutton switch for approximately 2 seconds. Re-
lease the switch when the LED is turned off. The diagnostic
LED will then display the flash codes associated with the last
five detected faults. The order of display is the most recent fault
to the least recent fault.