Greenheck IG / IGX (464104 IOM) (Pre-2009) - Manual (Page 57)

57
Operation - 8:1 Staged Control
Optional Exhaust fan switch (S1) manually closed
• Power passes through N.C. exhaust fan overload (ST2 O.L.) which is closed if supply fan (M1) 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 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 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 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 starter (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 (CH)
• 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) when needed
Ignition Controller (IC1) Sequence of Operation
• The N.O. air proving switch (PSH#) is open
• The ignition controller (IC1) energizes the combustion blower (CM1)
• The N.O. air proving switch (PSH#) closes
• The ignition controller completes a 30 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
• The controller will choose which stage to light the furnace at, based on the discharge air temperature set point
and the outside air temperature
• When a flame is detected the igniter stops sparking
• The furnace will remain at high fire for 20 seconds
• The stage controller (FX) will stage the gas valves (MV#) as needed between low fire, high fire and off
• The stage controller (FX) will monitor the pressure switch (PSH#) and shut down the furnace if the furnace is at
high fire and the high pressure switch is not satisfied
• If the furnace is at low fire and the discharge temperature remains above the set point for more than six
minutes the furnace will shut down
Staging Sequence of Operation
• If the temperature is more than 1ºF below the discharge air temperature setting the furnace will stage up
• If the temperature is more than 1ºF above the discharge air temperature setting the furnace will stage down
• If the temperature is above the set temperature and the furnace is at low fire, the furnace will shut off
• The furnace will not stage consecutively in the same direction more than once every six minutes
• If the furnace is at high fire and the discharge air temperature setting is not satisfied, the furnace will remain at
high fire
• If the furnace is at low fire and the discharge air temperature setting is satisfied, the furnace will shut off
Sequence of Operation
Operation