39
OPERATIONAL CHECKS
The burner flames should be inspected with the burner
compartment door installed. Flames should be stable,
quiet, soft, and blue (dust may cause orange tips but
they must not be yellow). Flames should extend directly
outward from the burners without curling, floating, or lifting
off. Flames must not impinge on the sides of the heat
exchanger firing tubes.
SAFETY CIRCUIT DESCRIPTION
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.
WARNING
Do not bypass any safety circuit.
Integrated Control Module
The integrated control module is an electronic device
which, if a potential safety concern is detected, 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 a normally-closed (electrically), automatic reset,
temperature-activated sensor. The limit guards against
overheating as a result of insufficient conditioned air
passing over the heat exchanger.
Auxiliary Limit
The auxiliary limit controls are located on or near the
circulator blower and monitors blower compartment
temperatures. They are a normally-closed (electrically),
manual-reset sensors. These limits guard against
overheating as a result of insufficient conditioned air
passing over the heat exchanger.
Rollout Limit
The rollout limit controls are mounted on the burner/
manifold assembly 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.
Pressure Switches
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 (combustion
air and flue products) through the heat exchanger and/or
blocked condensate drain conditions.
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.
MAINTENANCE
Annual Inspection
The furnace should be inspected by a qualified installer, or
service agency at least once per year. This check should
be performed at the beginning of the heating season.
This will ensure that all furnace components are in proper
working order and that the heating system functions
appropriately. Pay particular attention to the following
items. Repair or service as necessary.
• Flue pipe system. Check for blockage and/or leakage.
Check the outside termination and the connections at
and internal to the furnace.
• Heat exchanger. Check for corrosion and/or buildup
within the heat exchanger passageways.
•
Burners. Check for proper ignition, burner flame, and
flame sense.
• Drainage system. Check for blockage and/or leakage.
Check hose connections at and internal to furnace.
• Wiring. Check electrical connections for tightness
and/or corrosion. Check wires for damage.
• Filters.
FILTERS
Filter Maintenance
Improper filter maintenance is the most common cause of
inadequate heating or cooling performance. Filters should
be cleaned (permanent) or replaced (disposable) every
two months or as required. When replacing a filter, it must
be replaced with a filter of the same type and size.
Filter Removal
Depending on the installation, differing filter arrangements
can be applied. Filters can be installed in either the central
return register or a side panel external filter rack (upflow
only). A media air filter or electronic air cleaner can be
used as an alternate filter. Follow the filter sizes given in
the Recommended Minimum Filter size table to ensure
proper unit performance.
To remove filters from an external filter rack in an upright
upflow installation, follow the directions provided with
external filter rack kit.
