Direct Gas Make-Up Air
40
OPTIONAL EXHAUST
Exhaust Fan Contact (S1) Closed (optional)
• Power passes to normally closed exhaust overload
contact (ST2 OL).
• Power passes to exhaust starter(s) ST2.
• Normally open exhaust starters are energized and
closed.
• Power passes to exhaust fans.
• Exhaust fan(s) (M2) start.
SUPPLY FAN
Supply Fan Contact (S2) Closed
• Power passes through normally closed field-
supplied fire system contact (FSC).
• Power passes through normally open exhaust fan
contact (ST2), which is closed when the exhaust
relay (ST2) is activated (optional).
• Power passes to normally closed supply overload
contact (ST1 OL or VFD).
• Power passes through normally closed 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, optional normally
open damper limit switch (DL1) closes.
• Power passes to and energizes supply starter relay
(RF).
• Power passes to normally open fan contact (RF),
which is energized and closed.
• Supply starter (ST1) or variable frequency drive
(VFD) is energized.
• Supply starter contact (ST1) closes or VFD is
energized and power reaches and energizes
supply fan.
• Supply fan (M1) starts.
HEATING
Heat Contact (S4) Closed
• Power passes to normally open fan relay (RF or
ST1) which is energized and closed.
• Power passes to optional inlet air sensor contact
(TS4) which is closed if the inlet air temperature is
below the set point.
• Power passes to and energizes the heat relay (RH).
• Normally open heat relay contact (RH) closes.
Commercial Flame Safeguard Ignition Sequence
• Power passes to normally closed high limit control
contact (HLC1) which is closed if temperature has
remained below set point.
• Power passes to optional normally open and
normally closed high and low gas pressure
contacts (PS4 and PS3), which are both closed if
gas pressure is within the set range.
• Power passes to normally open and normally
closed airflow switches (PS2) which are closed if
there is proper airflow across the burner.
• Power passes to terminal TH on the flame
safeguard (FSG).
• Flame safeguard checks for proper airflow and
completes verification of no flame present at
burner.
• A 15 second prepurge is initiated.
• Power is passed to normally closed gas valve
(V2) which opens and the spark generator (SG) is
energized.
• The trial for ignition will last for up to 30 seconds or
until flame is confirmed.
• Spark generator (SG) is de-energized.
• The flame and airflow are continuously monitored.
Industrial Flame Safeguard Ignition Sequence
• Power passes to and energizes terminal 5 of the
flame safeguard (FSG). Power light on FSG is on.
• Power passes to normally closed high limit control
contact (HLC1) which is closed if temperature has
remained below set point.
• Power passes to optional normally open and
normally closed high and low gas pressure
contacts (PS4 and PS3), which are both closed if
gas pressure is within the set range.
• Power passes to terminal 6 of the flame safeguard
(FSG).
• Flame safeguard checks for proper airflow and
completes verification of no flame present at
burner.
• A 10 second prepurge is initiated.
• Power is passed to normally closed pilot gas valve
(V1) which opens and the spark generator (SG) is
energized.
• The trial for ignition will last for up to 10 seconds or
until flame is confirmed.
• After flame is confirmed, power is passed to the
normally closed main gas valves (V2) which open.
• Spark generator (SG) is de-energized.
• The flame and airflow are continuously monitored.
• A self-diagnostic check is performed every five
seconds.
Sequence of Operation
If the unit has a microprocessor, reference the
supplemental
Microprocessor Controller for Make-Up
Air Reference Guide
for more information.
