28
18-EB32D1-1E-EN
Sequence of Operation
Operation of the unit heating or cooling cycles is
controlled by the setting of the comfort control. Once
the comfort control is set to either HEAT or COOL, unit
operation is automatic. A fan setting on the comfort
control also provides for continuous operation of the
indoor fan when desired. The fan, when set to ON
provides continuous operation at constant circulation
of 40 - 50% nominal airflow at selected dipswitch
setting, while AUTO provides operation during the
heating or cooling cycles. CONTINUOUS fan mode
during COOLING operation may not be appropriate in
humid climates. If the indoor air exceeds 60% relative
humidity or simply feels uncomfortably humid, it is
recommended that the fan only be used in the AUTO
mode.
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(R) and (W1) thermostat contacts close signaling the
control module (IGN) to run its self-check routine. After
the control has verified that the pressure switch (PS)
contacts are open, the limit switch (TCO) contacts are
closed, and the flame rollout (FL) switch is closed, the
induced draft blower (CBM) will be energized on high
speed for approximately 5 seconds.
After the induced draft blower (CBM) has come up to
speed, the control will verify that the pressure switch
(PS) contacts are closed and switch the induced draft
blower to low speed for 20 second prepurge. The gas
valve (GV) is energized in the first stage to permit gas
flow and the spark igniter (IP) is energized. The flame
detector (FD) confirms that ignition has been achieved
within the 7 second trial period.
As the flame detector confirms that ignition has been
achieved the delay to indoor fan on period begins
timing and after approximately 45 seconds, the indoor
blower motor (IDM) will be energized at low speed and
will continue to run during the heating cycle.
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(R) and (W2) thermostat contacts close signaling a call
for second stage heat. The induced draft motor (CBM)
is energized on high speed and the gas valve on
second stage. After approximately 30 seconds the
control energizes the indoor blower on high speed.
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(R) and (W2) opens, the induced draft blower is
reduced to low speed the gas valve is reduced to first
stage. After about 30 seconds the indoor blower motor
is reduced to low speed.
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(R) and (W1) opens, the gas valve (GV) will close. The
induced draft blower (CBM) will be de-energized after
approximately 5 seconds postpurge. The indoor blower
motor (IDM) will continue to run for the fan off period
(field selectable 60 or 90 seconds [by jumpers]), then
will be de-energized by the control module.
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(R) and (W1/W2) (jumped) thermostat contacts close
signaling a call for heat. 1st stage sequence of
operation remains the same as above. 2nd stage heat
has a 10 minute delay from the time of 1st stage
ignition.
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(R) and (W1/W2) (jumped) contacts open signaling the
control module to close the gas valve and de-energize
the induced draft blower after approximately 5 second
postpurge. The I.D. blower motor will continue to
operate at the current speed for 60 or 90 seconds after
the flames are extinguished .
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This product is equipped with safety devices to protect
against abnormal conditions.
The temperature limit switch (TCO) is located on the
blower barrier, and can be accessed through the
blower compartment. This automatic reset device
protects against excessive supply air temperature. If
this device opens, the gas valve is immediately closed
and will not permit operation until the limit switch
closes.
The rollout switch (RO) is located in the gas
compartment near the inlet of the burners. This is a
manual reset device designed to protect against any
form of flame rollout. If this device is opened the gas
valve is immediately de-energized and the control
(IGN) will lockout the system. The rollout switch (RO)
must be reset before operation is allowed to continue.
The pressure switch (PS) is located in the upper right
side of the gas compartment. This automatic device
assures adequate combustion air pressure. If pressure
against the induced draft blower outlet becomes
excessive, the pressure switch will react and shut off
the gas valve, until acceptable combustion pressure is
again available.
If the control (IGN) does not sense flame within the first
trial for ignition period, the gas valve will be de-
energized. The control (IGN) will initiate a 60-second
interpurge. Following the interpurge, the control will
perform a second ignition attempt. If the second try is
not successful, the control will start another 60-second
interpurge. After the interpurge, a third attempt will be
tried. If the third try is not successful, the control will
lock out.
If loss of flame occurs during a heating cycle, the
control (IGN) will close the gas valve and cycle through
the ignition trial as stated above.
