User Guide

577C--K Ultra Low NOx: Product Data
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
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Controls
Operating Sequence
Heating Sequence of Operation (Ultra Low NOx Single
and Three Phase Models)
On a call for heating, terminal W of the thermostat is energized, starting
the induced-draft motor for a 30 second pre-purge at intermediate speed.
When the pressure switch senses that the induced-draft motor is moving
sufficient combustion air, the burner sequence begins. This function is
controlled by the integrated gas unit controller (IGC).
After 30 sec of pre-purge is complete, the pressure switch checks for
sufficient combustion. Then, the gas valve energizes and the system
attempts to ignite with igniter being energized. The igniter energizes for
5 sec and integrated gas controller (IGC) allows system to sense flame
for 2 sec at the end of 5 sec of ignition trial. On first successful ignition,
system stays at the intermediate inducer speed for 10 sec and gradually
ramps up to the high speed for steady-state operation. The system uses
the same logic for 2nd ignition trial. If a 3rd or 4th ignition attempt is
needed, the inducer speed is decreased to the low speed. On a successful
light on the 3rd or 4th attempt, the inducer speed is increased to the
intermediate speed for about 10 seconds and then gradually ramps up to
the high speed for steady-state operation. In case the 4th attempt fails,
the system will lock out for 1 hr. After 1 hr. lock out period, the system
starts with normal operating sequence. Once flame is established and
proven successfully, indoor (evaporator) fan motor is energized after 30
seconds. When the thermostat is satisfied and W is de-energized, the
pre-mix burner will stop firing and the indoor (evaporator) fan motor
shuts off after a 90 second time-off delay. Please note that the IGC has
the capability to automatically decrease the indoor (evaporator) fan
motor "ON" delay and increase the indoor (evaporator) fan motor "OFF"
delay in the event of high duct static and/or partially-clogged filter.
Cooling Sequence of Operation
With the room thermostat SYSTEM switch in the COOL position and
the FAN switch in the AUTO position, the cooling sequence of operation
is as follows:
1. When the room temperature rises to a point that is slightly above
the cooling control setting of the thermostat, the thermostat
completes the circuit between thermostat terminal R to terminals Y
and G.
2. The normally open contacts of energized contactor (C) close and
complete the circuit through compressor motor (COMP) to
condenser (outdoor) fan motor (OFM). Both motors start instantly.
3. The set of normally open contacts on the interface fan board (IFB)
are closed which energizes a circuit to the indoor fan motor (IFM).
NOTE: Once the compressor has started and then stopped, it should not
be started again until 5 minutes have elapsed. The cooling cycle remains
on until the room temperature drops to a point that is slightly below the
cooling control setting of the room thermostat. At this point, the
thermostat breaks the circuit between thermostat terminal R to terminals
Y and G. These open circuits deenergize contactor coil C. The condenser
and compressor motors stop. After a 60-sec. delay, the blower motor
stops. The unit is in a standby condition, waiting for the next call for
cooling from the room thermostat.