3a. Heat Contact S4 Closed Pilot Ignition

•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

3a. Heat Contact (S4) Closed - Pilot Ignition

•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 and energizes terminal 5 of the

Flame Safeguard (FSG). Power light on FSG is on.

•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 terminal 6 of the Flame

Safeguard (FSG)

•Power begins direct gas burner sequence

(see Direct Gas Burner Sequence)

3b. Heat Contact (S4) Closed - Direct Spark

•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)

Direct Gas Burner Sequence - Pilot Ignition

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.

Direct Gas Burner Sequence - Direct Spark