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NORA Oilheat Technicians Manual

Chapter 12 Limit Controls/Thermostats Chapter 12—Limit Controls and Thermostats 12-21 the interface between the thermostat and the air handler. They have an isolated end switch to start the boiler and/or circulator. When the thermostat calls for heat, the fan control energizes the end switch relay and allows the fan to operate at low speed when the water temperature is above the aquastat setting. When the thermostat calls for cooling, the fan control energizes the condenser and operates on high speed. Many of these relays also allow selectable one, three, four minute delay on fan operation in the heating mode.Many of these relays also allow selectable one, three, and four minute delay on fan operation in the heating mode. Combination controls When the controls are separate units and scattered around the boiler, they are referred to as non-integral controls. When they are all in one box, high limit, low limit and circulator controls are called integral controls. They are also available in dual capacity high limit and low limit, or as triple function controls acting as high limit, low limit, and reverse-acting circulator limit. In older heating systems, non-integrated control systems were used much more than they are now. Today’s systems are generally integrated control systems that provide control of both the burner and circulator by Figure 12-31: Diagram of typical hydro fan control (Both HAFC 101 and HAFC 201 are capable of 1 and 2 speed applications) HAFC 201 With 1 Speed Air Handler HAFC 101 With 2 Speed Air Handler


NORA Oilheat Technicians Manual
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