Safety Circuit Description; General; Integrated Control Module; Primary Limit - Goodman GMH8 Installation Instructions Manual

XIV. SAFETY CIRCUIT DESCRIPTION
GENERAL
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 continuously monitored
during furnace operation by the integrated control module.
INTEGRATED CONTROL MODULE
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
precautions and provide diagnostic information through an LED.
PRIMARY LIMIT
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
heat exchanger.
AUXILIARY LIMIT
The auxiliary limit control is located either on or near the circulator
blower and monitors heat exchanger compartment temperatures.
The control is an automatic reset, temperature sensor. It guards
against overheating resulting from insufficient air passing over
the heat exchanger.
ROLLOUT LIMITS
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.
PRESSURE SWITCHES
The pressure switches are normally-open, negative air pressure-
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.
FLAME SENSOR
The flame sensor is a probe mounted to the burner/manifold
assembly which uses the principle of flame rectification to
determine the presence or absence of flame.
XV. TROUBLESHOOTING
ELECTROSTATIC DISCHARGE
(ESD)
PRECAUTIONS
NOTE: Discharge body's static electricity before touching unit. An
electrostatic discharge can adversely affect electrical components.
Use the following precautions during furnace installation and
servicing to protect the integrated control module from damage.
By putting the furnace, the control, and the person at the same
electrostatic potential, these steps will help avoid exposing the
integrated control module to electrostatic discharge. This
procedure is applicable to both installed and uninstalled
(ungrounded) furnaces.
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 ungrounded
object.
DIAGNOSTIC CHART
Refer to the troubleshooting chart on the following pages for
assistance 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.
FAULT RECALL
The ignition control is equipped with a momentary pushbutton
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. Depress the
pushbutton switch for approximately 2 seconds. Release 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.
RESETTING FROM LOCKOUT
Furnace lockout results when a furnace is unable to achieve
ignition after three attempts. It is characterized by a non-functioning
furnace and a one flash diagnostic LED code from the red LED. If
the furnace is in "lockout", it will (or can be) reset in any of the
following ways.
1. Automatic reset. The integrated control module will
automatically reset itself and attempt to resume normal
operations following a one hour lockout period.
2. Manual power interruption, interrupt 115 volt power to the
furnace for 1 - 20 seconds.
3. Manual thermostat cycle. Lower the thermostat so that
there is no longer a call for heat for 1 - 20 seconds then
reset to previous setting.
NOTE: If the condition which originally caused the lockout still
exists, the control will return to lockout. Refer to the Diagnostic
Chart for aid in determining the cause.
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