Operation - Electrical
Electrical Sequence
1.Exhaust Fan Contact (S1) Closed (optional)
•Power passes through N.C. contact on exhaust fan overload (ST2 OL), which is closed if exhaust fan (M2) has not overloaded
•Power passes to exhaust fan starter (ST2)
•N.O. contact on exhaust fan starter (ST2) is energized and closed
•Power passes to exhaust fan
•Exhaust fan (M2) starts
2.Supply Fan Contact (S2) Closed
•Power passes through N.C. field supplied fire contact (FSC)
•Power passes through optional N.O. contact on exhaust fan starter (ST2), which is closed when the optional exhaust starter (ST2) is activated
•Power passes through N.C. contact on supply starter overload (ST1 OL), which is closed if the supply fan has not overloaded
•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 and energizes optional inlet damper (D1), which opens
•Power passes through optional N.O. damper limit switch (DL1), which is energized and closed when the optional inlet damper is open. It may take several minutes for the damper to fully open and for the damper limit switch to close
•Power passes to and energizes fan relay (RF)
•Power passes through N.O. contact on fan relay
(RF), which closes when the fan relay (RF) is energized
•Power passes to and energizes supply fan starter (ST1)
•N.O. contact on supply fan starter (ST1) is energized and closed
•Supply fan (M1) starts
3.Electric Heat Contact (S4) Closed (optional)
•Power passes through N.O. contact on fan relay
(RF), which is energized and closed
•Power passes through N.C. contact on optional inlet air sensor (TS4), which is closed if the inlet air temperature is below the set point
•Power passes to and energizes heat relay (RH)
•Power passes through N.O. contact on heat relay (RH), which closes when the heat relay (RH) is energized
•Power passes through N.O. contact on pressure
differential switch (PDS), which closes when proper airflow is achieved
•Power passes through N.C. automatic and manual reset temperature cutouts (A and M), which remain closed if the maximum temperature has not been reached
•Power passes to and energizes operating contactor relay (C1)
•Power passes through N.O. contacts on operating contactor (C1), which is closed
•Electric heater modulates/stages to maintain temperature set point
4.Evaporative Cooling Contact (S4) Closed* (optional)
•N.O. contact on fan relay (RF) is energized and closed
•Power passes through N.O. contact on optional inlet air sensor (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)
*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.
24 | Model MSX | ® |
