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NORA Oilheat Technicians Manual

wise direction until the scale plate had traveled below 175ºF. Once this point has been reached, line voltage power would once again be restored to the primary control and if the room thermostat is still calling for heat, the burner would once again operate. Always consult local codes and ordinances or regulations and manufacturer’s instructions before installing a fan limit control. The helical element of the fan limit control must be located in the furnace plenum or at a location where it will be subjected to a representative airflow and temperature. It must not be located near cold air returns or the humidifier, nor in a dead air spot where there is poor circulation. It must definitely not touch any internal parts of the furnace. Chapter 12 Limit Controls/Thermostats Figure 12-12 Types of Systems Limit Fan = On Fan = Off Average furnace, average system 200°F 140°F 110°F Oversized furnace and/or oversized fan and/or short air ducts 170°F 130°F 90°F Undersized furnace and/or undersized fan and/or long air ducts 230°F 160°F 130°F Figure 12-11 is a schematic wiring diagram showing how a Honeywell L4064B combination control is wired into the heating system electrical circuit. In this illustration, the limit control is wired directly into the hot line of the line voltage circuit and is in series with the primary control. The high limit control should never be wired to the neutral wire of the furnace unit. Figure 12-12 lists some typical warm air limit settings and fan control on and off settings; the lower these settings can be Warm Air Limit Settings without creating uncomfortably cool air delivery into the living area, the more economical the operation of the heating system will be. Referring to Figure 12-11, note that the fan motor is wired into the system circuit Figure 12-11: Warm air circuit Oil-Fired Forced Warm Air System Stack Detector Thermostat Primary Control Ignition Transformer Chapter 12—Limit Controls and Thermostats 12-11 Fan and High Limit Control Burner Motor Fan Motor Limit L2 L1 (Hot) Fan Power Supply


NORA Oilheat Technicians Manual
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