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With a properly designed system, the proper amount of
temperature rise will normally be obtained when the unit
is operated at rated input with the recommended blower
speed.
If the correct amount of temperature rise is not obtained, it
may be necessary to change the blower speed. A higher
blower speed will lower the temperature rise. A slower
blower speed will increase the temperature rise.
NOTE: Blower speed MUST be set to give the
correct air temperature rise through the unit as
marked on the rating plate.
NORMAL SEQUENCE OF OPERATION
Heating
This unit has one (RS) Manual Reset Limit Control Switch.
Check the limit to make sure it has not tripped. The limit
may arrive at the job site tripped as a result of shipping
shock.
If the venter motor comes on, but the unit does not attempt
ignition, check if the ALS (Auxiliary High Limit Control
Switch) requires resetting.
1. With electricity and gas turned on, the system switch
in the "HEAT" or "AUTO" position and the fan switch
in the "AUTO" position, the thermostat will close the
circuit between unit terminals R and W (R-W) when
the temperature falls below the thermostat setting.
2. D1 on IIC energizes venter motor contactor.
3. Venter motor contactor energizes the venter motor.
4. Operation of the venter motor closes the pressure
switch PS located in the burner compartment.
Unless excessive temperatures or shipping shock
have opened high limit control ALS, power is fed to
the integrated ignition control, which then initiates a
15-second pre-purge time delay. During this period,
the venter fan will clear the combustion chamber of
any residual gas.
5. After the pre-purge period, the ignition control
energizes the Wl-C gas valve and simultaneously
initiates a "three (3)-try" spark ignition sequence.
6. When the burners are ignited, a minimum one (1)
micro-amp DC current will flow through the flame
between the sensor electrode and the grounded
burner.
7. When the controller proves that the flame has been
established, it will keep the gas valve energized and
discontinue the ignition spark.
8. If the control is unable to ignite the burners after its
initial attempt, it will initiate another purge and spark
sequence. A third purge and spark sequence will
be initiated if the second attempt is unsuccessful.
If the third attempt is unsuccessful, the controller
will close the gas valve and lock itself out. It may be
reset by momentarily interrupting power. This may be
accomplished by briefly lowering the room thermostat
set-point below room temperature, or by shutting off
the main power to the unit.
9. Integrated ignition control will close its normally open
contacts after a delay of approximately 30 seconds.
This action energizes the blower motor contactor and
starts the supply fan motor. Operation of the supply
fan circulates air across the heat exchanger and
delivers heated air to the conditioned space.
10. When the space temperature rises, the thermostat will
open R-W. Opening R-W will cause the gas valve to
close, and the furnace to shut down.
11. The furnace has three high temperature limit controls,
which can shut down the burner. They do not shut
down the venter motor.
Unit Shutdown
1. Set the room heating setpoint to lowest setting.
2. Turn off the electrical power supply to the unit.
3. Remove the heat exchanger door on the side of the
unit by removing screws.
4. Move the gas control valve switch to the OFF position.
5. Close manual gas shut off valve external to the unit.
6. Replace the heat exchanger door on the unit.
7. If cooling and/or air circulation will be desired, turn
ON gas control valve switch and the electrical power.
Automatic Reset High Limit Control (LS)
Located in the burner compartment on the heat exchanger,
its sensing element projects through the blower section
bulkhead and senses the temperature at the rear of the
furnace. It will cycle the furnace off if the temperature
exceeds 100°F plus maximum rise.
Auxiliary High Limit Control (ALS)
Located in the blower compartment on the blower housing,
it senses air temperature within the blower compartment
and protects the filters from excessive temperature. It will
shut down the furnace if it senses excessive temperatures.
Elevated temperatures at the control are normally caused
by blower failure. The reason for the shut down should be
determined and repaired prior to resetting.
Manual Reset Flame Rollout Control (RS)
Located in the burner compartment at the top of the burner
assembly, it senses high temperature that could occur if
the heat exchanger tubes were plugged and the flame was
rolling out instead of entering the tubes. It has a manual
push-button reset that cannot be actuated until the limit
control has cooled.
The reason for elevated temperatures at the control should
be determined and repaired prior to resetting this manual
reset control.
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