Sequence of Operation
2:1 Staged Sequence
1.Exhaust Fan Contact (S1) Manually Closed (optional)
•Power passes through N.C. contact on exhaust fan overload (ST2 OL), which is closed if exhaust fan (M2) has not overloaded
•Power passes to exhaust fan starter (ST2)
•N.O. contact on exhaust fan starter (ST2) is energized and closed
•Power passes to and energizes exhaust fan (M2)
2. Supply Fan Contact (S2) Manually Closed
•Power passes through N.C.
•Power passes through optional N.O. contact on exhaust fan starter (ST2), which is closed when the optional exhaust starter (ST2) is activated
•Power passes through N.C. contact on supply starter overload (ST1 OL), which is closed if the supply fan has not overloaded
•Power passes through N.C. contact on optional freeze protection timer (RT4), which is closed if the temperature has remained above the set point
•Power passes to and energizes optional inlet damper (D1), which opens
•Power passes through optional damper limit switch
(DL1), which is energized and closed if the optional inlet damper is open. It may take several minutes for the damper to fully open and for the damper limit switch to close
•Power passes to and energizes fan relay (RF)
•Power passes through N.O. contact on fan relay
(RF), which is closed once the fan relay (RF) is activated
•Power passes to and energizes starter relay (ST1)
•N.O. contact on supply fan starter (ST1) is energized and closed
•Supply fan (M1) starts
3. Heat Contact (S4) Manually Closed
•Power passes through N.O. fan relay (RF), which is energized and closed if the supply fan (M1) is on
•Power passes through N.C. contact on optional inlet air sensor (TS4), which is closed if inlet air temperature is below the set point
•Power passes to and energizes the heat relay (RH)
•N.O. contact on heat relay (RH) closes
•24 VAC is supplied to stage controller (SC1)
•If the discharge temperature is less than the set point on the discharge air sensor (TS2) and the high temperature limit control (HLC1) has not been tripped, the N.O. contact for furnace stage controller will close
•Power will be supplied to the ignition controller
(IC1), which will begin its sequence of operation
4. Ignition Controller (IC1) Sequence of Operation
•The N.O. contact on air proving switch (PS2) is open
•The ignition controller (IC1) energizes the combustion blower relay (CR)
•N.O. contact on combustion blower relay (CR) closes
•Power passes to and energizes the combustion blower (CM)
•The N.O. contact on air proving switch (PS2) closes
•The ignition controller (IC1) begins a 15 second
•The high fire relay (RT3) is energized and the N.O. contact on high fire relay (RT3) closes
•The main gas valve (MV) fully opens (100%)
•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 at least 10 seconds
•High fire contact (RT3) will open
•Furnace stages to maintain the discharge air temperature set point (SC1)
5. 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 is above the discharge air sensor (TS2) set point, the N.O. furnace stage 2 controller contact (SC2), will open and the furnace will go to low fire (50%)
•If the furnace is at low fire (50%) and the discharge temperature is above the discharge air sensor (TS2) set point, the furnace stage 1 contact (SC1) will open and the furnace will shut down
•If the furnace is at low fire (50%) and the discharge temperature is below the discharge air sensor (TS2) set point, the furnace stage 2 contact (SC2) will close and the furnace will go to high fire
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 optional 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.
38 Model IG / IGX
®
