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4. Ignition Controller (IC1) Sequence of Operation
• The N.O. contact on air proving switch (PS2) is open
• The ignition controller (IC1) energizes the induction
relay (IR)
• N.O. contact on induction relay (IR) closes
• Power passes to and energizes the combustion
blower (CM), sending it to high speed
• The N.O. contact on air proving switch (PS2) and
high pressure switch (PS5) closes
• The ignition controller (IC1) begins a 15 second
pre-purge
• The main gas valve (MV) fully opens (100%) and the
modulating gas valve (MOD) opens to high fire
• Igniter begins sparking
• 10 second trial for ignition begins
• The furnace will light at high fire (100%)
• When the flame is detected, the igniter stops
sparking
• The furnace will remain at high fire (100%) for 30
seconds
• The modulation controller (SC1) will adjust the
modulating gas valve (MOD) and the combustion
blower (CM) as needed between low and high fire
• The modulating controller (SC1) will monitor the
high pressure switch (PS5) and run the furnace at
low fire if the high pressure switch is not satisfied
5. High Fire – Low Fire Sequence of Operation
• The furnace lights at and remains at high fire
(100%) for 30 seconds
• If the discharge temperature sensor (TS2) reading
is above the discharge temperature setting (dtS,
FX Program Menu), and the furnace is not at low
fire, the modulating controller (SC1) will adjust
the modulating gas valve (MOD) down until the
discharge temperature sensor (TS2) reading
equals the discharge temperature setting (dtS, FX
Program Menu)
• If the discharge temperature sensor (TS2) reading
is below the discharge temperature setting (dtS,
FX Program Menu), and the furnace is not at high
fire, the modulating controller (SC1) will adjust the
modulating gas valve (MOD) up until the discharge
temperature sensor (TS2) reading equals the
discharge temperature setting (dtS, FX Program
Menu)
6. Optional Evaporative Cooling Contact (S4)
Closed*
• N.O. contact on fan relay (RF) is energized and
closed
• Power passes through N.O. contact on inlet air
sensor (TS4), which is energized and closed if the
inlet air temperature is above the set point
• Power passes to and energizes cool relay (RC)
• N.O. contact on cool relay (RC) is energized and
closed
• Power passes to evaporative cooling pump (P1)
*If DX or chilled water coils are used rather than an
evaporative cooler, the cooling sequence of operation
will depend on the coil controls. Cooling coil controls are
supplied by others.
Sequence of Operation
4:1 Electronic Modulation,
continued
®
Model IG / IGX Make-Up Air
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