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nace has been operating (burners firing) for approximately ten min-
utes. Check the control as follows:
1. Allow the furnace to operate with burners firing continuously
for approximately ten minutes.
2. Gradually block the return air to furnace. Remove airflow
blockage when limit control is activated and turns off burners.
Airflow blockage causes unit overheating and will produce
the following reactions:
• The gas valve to close and extinguish flame,
• The induced draft blower to deenergized after a fifteen
second postpurge, and
• The circulator blower to remain energized continuously
until limit control resets.
NOTE: If testing is performed on high stage, the circulator blower
will switch to low stage speed following the selected heat off delay.
3. Remove the return air blockage to clear overheating condition.
After an acceptable temperature is reached during the cool
down period, the limit control will reset and allow the furnace
to resume normal operation.
These checks establish that the primary limit control is functioning
and will respond to a restriction in the return air, or a circulator blower
failure. If the primary limit control does not function during this test,
the cause must be determined and corrected.
XVII. SAFET
XVII. SAFET
XVII. SAFETY CIR
Y CIRCUIT DESCRIPTI
Y CIR
Y CIR
XVII. SAFET
XVII. SAFET
Y CIR
G
ENERAL
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 ab-
normal function. These circuits are continuously monitored during
furnace operation by the integrated control module.
I
C
M
NTEGRATED
ONTROL
ODULE
The integrated control module is an electronic device which, if a po-
tential safety concern is detected, will take the necessary precau-
tions and provide diagnostic information through an LED.
P
L
RIMARY
IMIT
The primary limit control is located on the partition panel and moni-
tors heat exchanger compartment temperatures. It is a normally-
closed (electrically), automatic reset, temperature-activated sensor.
The limit guards against the overheating as a result of insufficient
conditioned air passing over the heat exchanger.
A
L
UXILIARY
IMIT
The auxiliary limit controls are located on or near the circulator blower
and monitors blower compartment temperatures. They are a nor-
mally-closed (electrically), manual-reset sensors. These limits guard
against overheating as a result of insufficient conditioned air pass-
ing over the heat exchanger.
R
L
OLLOUT
IMIT
The rollout limit controls are mounted on the burner/manifold as-
sembly and monitor the burner flame. They are normally-closed
(electrically), manual-reset sensors. These limits guard against
burner flames not being properly drawn into the heat exchanger.
P
S
RESSURE
WITCHES
The pressure switches are normally-open (closed during operation)
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 and the coil front
cover. These switches guard against insufficient airflow (combus-
CUIT DESCRIPTI
CUIT DESCRIPTIO O O O O N N N N N
CUIT DESCRIPTI
CUIT DESCRIPTI
tion air and flue products) through the heat exchanger and/or blocked
condensate drain conditions.
F
S
LAME
ENSOR
The flame sensor is a probe mounted to the burner/manifold assem-
bly which uses the principle of flame rectification to determine the
presence or absence of flame.
XVIII. TR
XVIII. TR
XVIII. TROUBLESH
XVIII. TR
XVIII. TR
E
D
LECTROSTATIC
ISCHARGE
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 servic-
ing to protect the integrated control module from damage. By put-
ting the furnace, the control, and the person at the same electro-
static potential, these steps will help avoid exposing the integrated
control module to electrostatic discharge. This procedure is appli-
cable 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 furnaces
near 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.
D
C
IAGNOSTIC
HART
T
O AVOID ELECTRICAL SHOCK, INJURY OR DEATH, DISCONNECT ELECTRICAL
POWER BEFORE PERFORMING ANY SERVICE OR MAINTENANCE.
Refer to the Troubleshooting Chart at the end of this manual 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 refers to a specific fault code.
R
F
L
ESETTING
ROM
OCKOUT
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. 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 0 - 20 seconds.
3. Manual thermostat cycle. Lower the thermostat so that there
is no longer a call for heat then reset to previous setting.
Interrupt thermostat signal to the furnace for 0 - 20 seconds.
NOTE: If the condition which originally caused the lockout still exists,
the control will return to lockout. Refer to Section XVIII,
Troubleshooting - Diagnostic Chart for aid in determining the cause.
33
OUBLESH
OUBLESH
OUBLESHOO
OUBLESH
OOTIN
OO
OO
OO
TING G G G G
TIN
TIN
TIN
(ESD) P
RECAUTIONS
WARNING
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Table of Contents
Troubleshooting
