Greenheck IGK (472084) - Manual (Page 10)

10 Model IGK Make-Up Air
®
Sequence of Operation
2:1 Staged Sequence
1. Optional supply fan switch (S2) manually
closed
(If no supply fan switch is installed, power will
automatically be supplied to the supply starter
overload (ST1 OL) when the unit is powered)
• Power passes through N.C. supply starter overload
(ST1 OL) which is closed if the supply fan has not
overloaded
• Power reaches supply fan starter (ST1)
• N.O. supply fan starter (ST1) is energized and
closed
• Power passes through the N.O. supply starter
auxiliary contact (ST1 (AUX)) and energizes
optional inlet damper (D1) which opens
• Power reaches and energizes supply fan (M1)
2. Optional heat switch (S3) manually closed
(If no heat switch is installed, power will automatically
be supplied to the supply starter relay (ST1) when the
unit is powered)
• Power passes through the high temperature limit
switch (HLC) which is closed if the discharge
temperature is not higher than the high
temperature limit switch set point
• Power passes through N.O. supply fan starter relay
(ST1) which is energized and closed
• Power passes through the N.O. inlet air sensor
(TS1) which is closed if inlet air temperature has
remained below the set point
• Power passes to the discharge temperature stage
controllers (SC1 & SC2)
• If the discharge air temperature sensed by the
discharge air sensor (TS2) is less than the stage
one controller (SC1) set point, the furnace stage
one controller (SC1) N.O. contact will close,
powering the ignition controller (IC)
• If the discharge air temperature is also less than
the stage one controller (SC1) set point minus the
stage two controller (SC2) offset , the furnace stage
two controller (SC2) N.O. contact will also close
• The ignition controller (IC) will begin its sequence
of operation
3. Ignition Controller (IC) Sequence of Operation
• The N.O. air proving switch (PS2) is open
• The ignition controller (IC) energizes the
combustion blower (CM)
• The N.O. low air proving switch (PS2) closes
• The ignition controller completes a 15 second pre-
purge
• The high fire timer relay (RT3) is energized and the
N.O. contact passes power to the high fire terminal
on the combination gas valve (MV)
• The combination gas valve (MV) fully opens (100%)
• 10 second trial for ignition period begins
• Igniter (SPARK) begins sparking
• The furnace will light at high fire (100%)
• When the flame is detected by the flame sense
electrode (SENSOR) the igniter (SPARK) stops
sparking
• The furnace will remain at high fire (100%) for 10
seconds
• The high fire timer expires and the N.O. contact
opens, allowing the stage two controller (SC2) to
control the power to the high fire terminal of the
combination gas valve (MV)
4. High Fire – Low Fire Sequence of Operation
• The furnace lights at high fire (100%), and remains
at high fire for 10 seconds
• If the discharge temperature sensor (TS2) is above
the stage one controller (SC1) set point minus the
stage two controller (SC2) offset, the stage two
controller (SC2) contact will open and the furnace
will go to low fire (50%)
• If the furnace is at low fire (50%) and the discharge
temperature sensor (TS2) is above the stage one
controller (SC1) set point, the furnace stage one
controller (SC1) contact will open and the furnace
will shut down
• If the furnace is at low fire (50%), and the discharge
temperature sensor (TS2) remains below the stage
one controller (SC1) set point minus the stage
two controller (SC2) offset, the furnace stage two
controller (SC2) contact will close and the furnace
will go to high fire (100%)