Direct Spark Ignition Make-Up Air24
Direct Gas Burner Sequence
1. Supply Fan Contact Closed
• Power passes to the supply fan and heat switch
2. Heat Contact Closed
• Power passes to the heat relay then to the Flame
Safeguard
3. Flame Safeguard (FSG) Sequence
• Checks for proper airflow
• Verifies no flame present at burner
• Initiates 15 second prepurge
• Sends power to open gas valve (V2) and energizes
the spark generator
• Tries for up to 10 seconds to light and confirm
flame
• Shuts down spark generator
• Continuously monitors the flame and airflow
Electrical Sequence
1. Exhaust Fan Contact (S1) Closed (optional)
• Power passes to N.C. exhaust overload contact
(ST2 OL) (optional)
• Power passes to exhaust starter(s) ST2
• N.O. exhaust starter switches are energized and
closed
• Power passes to exhaust fans
• Exhaust fan(s) (M2) start
2. Supply Fan Contact (S2) Closed
• Power passes through N.C. field-supplied fire
contact (FSC)
• Power passes through N.O. exhaust fan contact
(ST2), which is closed when the exhaust relay (ST2)
is activated (optional)
• Power passes to N.C. supply overload contact
(ST1 OL)
• Power passes through N.C. contact on optional
freeze protection timer (RT4) which remains closed
if the temperature has remained above the set point
• Power passes to optional inlet damper which
opens
• When damper is fully opened, damper relay (D1) is
energized and optional N.O. damper limit switch
(DL1) closes
• Power passes to and energizes supply starter relay
(RF)
• Power passes to N.O. fan contact (RF), which is
energized and closed
• Supply starter (ST1) is energized
• Supply starter contact (ST1) closes and power
reaches and energizes supply fan
• Supply fan (M1) starts
3. Heat Contact (S4) Closed
• Power passes to N.O. fan relay (RF) which is
energized and closed
• Power passes to optional inlet air sensor contact
(TS4) which is energized and closed if the inlet air
temperature is below the set point
• Power passes to and energizes the heat relay (RH)
• N.O. heat relay contact (RH) closes
• Power passes to N.C. high limit control contact
(HLC1) which is closed if temperature has remained
below set point
• Power passes to optional N.O. and N.C. high and
low gas pressure contacts (PS4 and PS3), which
are both closed if gas pressure is within the set
range
• Power passes to N.O. and N.C. airflow switches
(PS2) which are closed if there is proper airflow
across the burner
• Power passes to terminal TH on the Flame
Safeguard (FSG) which begins it’s sequence
(see Direct Gas Burner Sequence)
4. Optional Evaporative Cooling Contact (S4)
Closed*
• N.O. contact on fan relay (RF) is energized and
closed
• Power passes to optional inlet air sensor contact
(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 optional 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.
Operation - Electrical
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