Greenheck IG / IGX (464104 IOM) (Pre-2009) - Manual (Page 56)

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Operation - 4:1 Electronic Modulation
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 optional N.O. exhaust fan contact (ST2) which is energized and closed
• Power passes through optional N.O. freeze protection contact (FZ1) which is closed if temperature has
remained above freeze protection set point
• Power passes to and energizes optional inlet damper (D1) which opens. Power also reaches 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 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 through call for heat relay (CH) which energizes and closes the N.O. call for heat contactor (Call
for Heat Contactor)
• The modulating controller (FX) compares the discharge temperature or space temperature to the set point and
sends a call for heat to the ignition controller (IC1)
Ignition Controller (IC1) Sequence of Operation
• The N.O. low air proving switch (PSL) is open
• The ignition controller (IC1) energizes the combustion blower (CM1)
• The N.O. low air proving switch (PSL) closes
• The ignition controller completes a 15 second pre-purge
• The main gas valve (MV1) is powered open
• 10 second trial for ignition period begins
• Igniter begins sparking
• The furnace will light at high fire
• When a flame is detected the igniter stops sparking
• The furnace will remain at high fire for 30 seconds
• The modulation controller (FX) will modulate the gas valve (MDV) and the combustion blower (CM1) as needed
between low fire and high fire
• The modulating controller (FX) will monitor the high pressure switch (PSH) and shut down the furnace if the
furnace is at high fire and the high pressure switch is not satisfied
High Fire – Low Fire Sequence of Operation
• The furnace lights at, and remains at high fire (100%) for 30 seconds
• If the discharge temperature is above the discharge temperature set point, and the furnace is not at low fire,
the modulation controller (FX) will modulate the gas valve (MDV) down until the discharge temperature equals
the discharge temperature setting.
• If the discharge temperature is below the discharge temperature set point, and the furnace is not at high fire,
the modulation controller (FX) will modulate the gas valve (MDV) up until the discharge temperature equals the
discharge temperature set point
Sequence of Operation
Operation