Greenheck DG / DGX Industrial Space Heating (464044 IOM) (Pre-2009) - Manual (Page 17)

Operation - Electrical without 7 Day Timer
1. Switch (S2) in Summer Mode
• Power passes to terminal G
• 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
2. Switch (S2) in Winter Mode
• If space temperature is less than the daytime temperature setting, the N.O. temperature sensor contact
(TS) closes
• Power passes to terminal W1 then to fan relay (R4)
• Fan relay (R4) is energized and N.O. contact (R4) closes
• Power passes to terminal G
• 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 and heat relay (R2)
• N.O. heat relay contact (R2) closes
• Power passes to and energizes terminal 5 of the Flame Safe Guard (FSG)
• Power passes to N.C. high limit control contact (HLC1) which is closed if the temperature has remained
below the HLC1 set point
• Power passes to N.O. and N.C. gas pressure contact(s) (PS1, PS3) which are both closed if gas pressure
is within the set range
• Power passes to terminal 6 of the FSG
• FSG begins direct gas burner sequence (see direct gas sequence)
3. Flame Safe Guard (FSG) Sequence
• Verifies proper airflow with airflow switch PS2
• Verifies no flame present at burner
• Initiates 10 second prepurge
• Sends power to open pilot valve (V1) and energizes the spark generator (SG1) (clicking of the spark
generator may be heard).
• Energizes spark generator for up to 10 seconds to light pilot and confirm flame.
• Powers the main gas valves (V2 and V3) open
• Shuts down spark generator
• Continuously monitors the flame and airflow
• Performs self-diagnostic check every four seconds
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