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Heating Sequence of Operation
When the thermostat calls for heating, R is closed to W. The
following describes the gas heating sequence of operation.
1. A call for heat from the room thermostat starts the
combustion air blower and the circulating air blower.
2. When the speed of the combustion air blower reaches
proper RPM, the pressure switch closes, initiating a
pre-purge period (30 seconds nominal).
3. When the pre-purge period has expired, the ignition
control energizes the main gas valve and spark
electrode for a period of 10 seconds.
4.
If the flame sensor does not sense that a flame has
been established in the 10-second interval, then the
ignition control will de-energize the gas valve, and
begins a 30 second inter-purge period, then initiates
another trial for ignition.
5. The ignition control is designed to repeat this “trial
for ignition” a total of three times. If, at the end of the
third trial, flame still has not been established, then the
ignition control will try to light again 1 hour later. The
1-hour retry is indefinite. The ignition control can be
reset by interrupting the unit power or the thermostat
circuit.
6.
Once flame sense has been established, the circulating
air blower is energized after a 30 second blower on
delay.
7.
When the thermostat is satisfied, the combustion air
blower and gas valve are de-energized. The circulation
air blower will continue to run for a short period after
the furnace is shut down.
Blower Delay – Heating
• The circulating air blower “OFF” delay is 120 seconds
after shutting down the burners. This delay is not
adjustable.
• The circulating air blower “ON” delay is 120 seconds
after “W” signal is received to allow the furnace to
warm up.
Safety Controls
The control circuit includes the following safety controls:
Limit Control
This control is located behind the heat exchanger access
panel and is designed to open at abnormally high circulating
air temperatures. It resets automatically. The limit control
operates when a high temperature condition, caused by
inadequate airflow, occurs. This closes the main gas valve.
Pressure Switch
If the combustion air blower should fail, the pressure
switch prevents the spark electrode and gas valve from
being energized.
Maintenance – Gas / Electric Units
Periodic inspection and maintenance normally consists of
changing or cleaning the filters and cleaning the evaporator
coil. On occasion, other components of the furnace may
also require cleaning.
Shut off all electrical power to the unit before conducting
any maintenance procedures. Failure to do so could
cause personal injury.
WARNING
Filters
Filters are not supplied with the unit. Inspect once a month.
Replace disposable or clean permanent type as necessary.
Do not replace permanent type with disposable.
Motors
Indoor and outdoor fan and vent motors are permanently
lubricated and require no maintenance.
Evaporator Coil
Dirt and debris should not be allowed to accumulate on
the evaporator coil surface or other parts in the air circuit.
Cleaning should be as often as necessary to keep coil
clean. Use a brush, vacuum cleaner attachment, or other
suitable means. If water is used to clean the coil, be sure
the power to unit is shut off prior to cleaning.
Care should
be used when cleaning the coil so that the coil fins are
not damaged.
Do not permit the hot condenser air discharge to be
obstructed by overhanging structures or shrubs.
Condenser Coil
Clean condenser coil annually with water and inspect
monthly during the cooling season.
Flame Sensor
If the ignition control does not receive a signal from the
flame sensor indicating that the burners have established
flame, the gas valve closes after the 10-second trial for
ignition period.
Rollout Switch
The switch is located on the top of the burner box. In the
event of a sustained main burner rollout, the rollout switch
shuts off the ignition control and closes the main gas valve.
To reset, push the button on top of the switch.
Secure Owner’s Approval
When the system is functioning properly, secure the owner’s
approval. Show the owner the location of all disconnect
switches and the thermostat. Instruct the owner on how
to start and stop the unit and how to adjust temperature
settings within the limitations of the system.
