27
CONTROLS
Sequence of Operation
Cooling Operation—With a call for first stage cooling, the outdoor
fan and low--stage compressor are energized. If low--stage cannot
satisfy cooling demand,high--stage isenergized by the UserInterface.
After second stage issatisfied, theunit returns to low--stage operation
until first stage is satisfied or until second stage is required again.
When both first stage and second stage cooling are satisfied, the
compressor will shut off.
NOTE: When two--stage unit is operating at low stage, system
vapor (suction) pressure will be higher than a standard
single--stage system or high--stage operation.
Gas Heat Mode and Adjustments—When the UI calls for gas heat,
the Evolution furnace board performs a self--check, verifies the
pressure switch is open, and starts the inducer on high speed.
1. Inducer Pre--purge Period: When theinducermotorcomesup
on high speed, the pressure switch closes, and the Evolution
ignition control on the furnace board begins a 15 second
pre--purgeperiod. Ifthepressureswitch failsto remainclosed,
the inducer will remain running. After the pressure switch
re--closes, the Evolution ignition control will begin a new 15
second pre--purge period.
2. Trial--For--Ignition Sequence: The spark igniter will spark for
3 sec. The main gas valve relay contact closes to energize the
gasvalveon low stage. After 5 sec, theigniter isde--energized
and a 2--second flame--proving period begins. NOTE: The
unit always lights on high speed inducer and low stage gas
valve operation.
3. Flame--Proving: When the burner flame is proved at the
flame--proving sensor, the furnace control determines what
heating stage to run based on feedback from the UI. If the UI
is asking for low stage gas heat, the ignition control will
change the inducer speed to low speed and keep the gas valve
energized on low stage. If the UI is asking for high stage gas
heat, the ignition control will maintain running the induceron
high speed and energize the gas valve’s high stage relay to
increase gas flow.
If the burner flame is not proved within 2 second, the control will
close the gas valve and repeat the ignition sequence up to 3 more
Trials--For--Ignition before going to Ignition--Lockout. Lockoutwill
reset automatically after3 hrs, by momentarily interrupting 230 VAC
power, or by interrupting 24 VAC power at SEC1 or SEC2 to the
furnace board.
Ifflameisproved when thereshould be no flamepresent, control will
lock out of Gas--Heating mode and operate the inducer motor until
flame is no longer proved.
4. The indoor (evaporator) fan motor is energized 30 seconds
after flame is established. When the UI is satisfied, the
burners stop firing and the indoor (evaporator) fan motor
shuts off after a field--selectable time off delay (90, 120, 150
or 180 seconds).
NOTE: If continuous fan is “ON”, the indoor (evaporator) fan
motor will switch to the gas heating speed on a call for heat and
will resume continuous fan speed, once the UI is satisfied.
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