Greenheck DGX Installation, Operation And Maintenance Manual page 30

Electrical Sequence
1. Exhaust Fan Switch (S1) Closed
• Power passes to exhaust starter(s) ST2(3)
• N.O. exhaust starter switches are energized
and closed
• Power passes to exhaust fans
• Exhaust fans start
2. Supply Fan Switch (S2) Closed
• N.O. contact(s) ST2(3) are closed
• Power passes to optional freeze protection
relay (FZ1) and if temperature is acceptable
N.C. contact (FZ1) remains closed
• Power passes to damper which opens
• When damper is fully opened, damper relay
(D1) is energized and N.O. damper limit switch
(DL1) closes.
• Power passes to and energizes supply starter
relay (ST1)
• Supply starter contact (ST1) closes and power
reaches and energizes supply fan
• Supply fan starts
3. Heat Switch (S3) Closed
• Power passes to N.O. ST1 which is energized
and closed
• Power passes to inlet air sensor contact (TS1)
which is energized and closed if proper inlet air
temperature is present
• Power passes to and energizes heat relay (R2)
• N.O. heat relay contact (R2) closes
• Power passes to N.C. high limit control contact
(HLC1) which is closed if temperature has
remained below set point
• Power passes to N.O. and N.C. gas pressure
contacts (PS1) which are both closed if gas
pressure is within the set range
• Power passes to N.O. and N.C. airflow switch
(PS2) which are closed if there is proper airflow
across the burner
• Power passes to terminal L1 on the FSG which
begins it's sequence (see direct gas sequence)
4. Evaporative Cooling Switch (S4)
Closed*
• N.O. contact ST1(AUX) is energized and closed
• Power passes to and energizes cool relay (R1)
• N.O. contact R1 is energized and closed
• Power passes to 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
30
Direct Gas Burner Sequence
1. Supply Fan Switch Closed
• Power passes to the supply fan and heat switch
2. Heat Switch Closed
• Power passes to the heat relay then to the
Flame Safe Guard
3. Flame Safe Guard (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 (clicking of the
spark generator may be heard).
• Tries for up to 10 seconds to light and confirm
flame.
• Shuts down spark generator
• Continuously monitors the flame and airflow