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NORA Oilheat Technicians Manual

Figure 12-13: Electronic fan timer in parallel with the primary control and the high limit control. The fan control should always be connected on a warm air system in this manner to enable the fan motor to operate independently of the burner. Electronic fan timer center Most new warm air furnaces incorporate air conditioning, heating, humidification and air cleaning in one unit. They also feature multi-speed direct drive blower motors. To operate all these devices, they need an electronic fan center. A good example of this device is the Honeywell ST9103A Electronic Fan Timer, Figure 12-13. It integrates the control of all burner and system fan operations in an oil furnace. This control serves as the central wiring point for most of the electric components of the furnace. The ST9103A allows the thermostat to control heating, cooling, and system fan demands and run the oilburner primary control as well as up to a four speed circulating fan. It also monitors a limit switch string, which energizes the circulating fan whenever the limit switch opens. Electronic air cleaner and humidifier convenience 12-12 Limit Controls and Thermostats terminal connections are provided as an option. A means for operating continuous indoor air circulation is also available as an option. See Figure 12-14 for ST9103A wiring connections and Table 12-1 for the operating sequence. Steam system controls Pressure controls Limit controls that respond to changes in steam pressure are called pressure controls, or pressuretrols. As is the case with warm air limit controls and hot water controls, Figure 12-14: Honeywell ST9103A wiring connections Chapter 12 Limit Controls/Thermostats


NORA Oilheat Technicians Manual
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