Greenheck Fan VSU Operation - Electrical, Supply Fan Contact S2 Closed, Heat Contact S4 Closed

Operation - Electrical

Electrical Sequence

1.Supply Fan Contact (S2) Closed

•Power passes to damper which opens

•When damper is fully opened, damper relay

(D1) is energized an optional N.O. damper limit switch (DL1) closes

•Power passes through a N.C. fault contact on soft starter (PST(FAULT))

•Power passes to and energizes supply fan relay

(RI)

•Supply fan starts

2.Heat Contact (S4) Closed

•Power passes to N.O. fan relay which is energized and closed

•Power passes to inlet air sensor contact (TS) 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 and energizes terminal 5 of the

Flame Safeguard (FSG).

•Power passes to N.C. high limit control contact

(HLC) which is closed if temperature has remained below the high limit set point

•Power passes to terminal 6 of the Flame

Safeguard (FSG)

•Flame Safeguard (FSG) begins direct gas burner sequence (see Direct Gas Burner sequence)

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 10 second prepurge

•Sends power to open pilot gas valve (V1) and energizes the spark generator (SG) (clicking of the spark generator may be heard)

•Tries for up to 10 seconds to light pilot and confirm flame

•Powers the main gas valves open

•Shuts down spark generator

•Continuously monitors the flame and airflow

•Performs self-diagnostic check every five seconds

Model VSU Make-Up Air 13

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