Greenheck TSU Base Unit Manual (464441) - Manual (Page 21)

Make-Up Air Unit 21
®
Operation - Electrical
Electrical Sequence
Exhaust Fan Contact (S1) Closed (optional)
• Power passes to N.C. exhaust overload contact
(ST2 OL) (optional)
• Power passes to exhaust starter(s) (ST2)
• N.O. exhaust starter switches are energized and
closed
• Power passes to exhaust fans
• Exhaust fan(s) (M2) start
Supply Fan Contact (S2) Closed
• Power passes through N.C. field-supplied fire
contact (FSC)
• Power passes through N.O. exhaust fan contact
(ST2) which is closed when the exhaust relay (ST2)
is activated (optional)
• Power passes to N.C. supply overload contact
(ST1OL)
• 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 (D1) which
opens
• When damper is fully opened, 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
Heat Contact (S4) Closed
• Power passes to N.O. fan relay (RF or ST1) 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)
Optional Evaporative Cooling Contact (S4)
Closed*
• N.O. contact on fan relay (RF) is energized and
closed
• Power passes to optional inlet air sensor contact
(TS4) which is energized and closed if the inlet air
temperature is above the set point
• Power passes to and energizes cool relay (RC)
• N.O. contact on cool relay (RC) is energized and
closed
• Power passes to optional evaporative cooling pump
(P1)
Direct Gas Burner Sequence
Supply Fan Contact Closed
• Power passes to the supply fan and heat switch
Heat Contact Closed
• Power passes to the heat relay then to the Flame
Safeguard
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)
• Tries for up to 10 seconds to light pilot and confirm
flame
• Powers the main gas valves (V2) open
• Shuts down spark generator (SG)
• Continuously monitors the flame and airflow
• Performs self-diagnostic check every five seconds