Greenheck IG / IGX (464104 IOM) (Pre-2009) - Manual (Page 53)

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Operation - 2:1 Modulating Sequence
Optional Exhaust fan switch (S1) manually closed
• Power passes through N.C. exhaust fan overload (ST2 O.L.) which is closed if exhaust fan (M2) has not
overloaded
• Power passes to exhaust fan starter (ST2)
• N.O. Exhaust fan starter contactor (ST2) is energized and closed
• Power passes to and energizes exhaust fan (M2)
Supply fan switch (S2) manually closed
• Power passes through N.C. field supplied fire contact (FSC)
• Power passes through the optional N.O. exhaust fan contact (ST2) which is energized and closed
• Power passes to the optional freeze protection (FZ1) and through N.C. freeze protection contact (FZ1) which is
closed if temperature has remained above set point
• Power passes to and energizes the optional inlet damper (D1) which opens. Power also reaches the optional
return air damper (D3) which will now modulate or open depending on control
• Power passes through damper limit switch (DL1) which is energized and closed if the 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 through N.C. supply starter overload (ST1 O.L.) 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 reaches and energizes supply fan (M1)
Heat switch (S3) manually closed
• Power passes through N.O. supply fan contact (ST1) which is energized and closed
• Power passes to the amplifier
• If the discharge air sensor (TS2) reading is less than the temperature selector (TS3) setting, the amplifier sends
a call for heating to the ignition controller (IC1)
Ignition Controller (IC1) Sequence of Operation
• The N.O. low air proving switch (PS2) is open
• The ignition controller (IC1) energizes the combustion blower (CM1)
• The N.O. low air proving switch (PS2) closes
• The ignition controller completes a 15 second pre-purge
• The high fire relay (T2) is energized and the high fire contact (T2) closes
• The main gas valve (MV2) fully opens (100%)
• 10 second trial for ignition period begins
• Igniter begins sparking
• 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 (T2) will open
High Fire – Low Fire Sequence of Operation
• The furnace lights at, and remains at high fire (100%) for 10 seconds
• If the discharge temperature sensor (TS2) is above the temperature selector (TS3) set point, and the furnace is
not at low fire, the amplifier will modulate the gas valve (MDV) down until the discharge air sensor (TS2) reading
equals the temperature selector (TS3) setting
• If the discharge temperature sensor (TS2) is below the temperature selector (TS3) set point, and the furnace is
not at high fire, the amplifier will modulate the gas valve (MDV) up until the discharge temperature sensor (TS2)
reading equals the temperature selector (TS2) set point
• If the furnace is at low fire and the discharge air sensor (TS2) is above the temperature selector (TS3) set point
the amplifier will end the call for heat and the ignition controller (IC1) will shut down the furnace
Sequence of Operation
Operation