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I-SCE (09-18) PN207697R9
Figure 24. Unit-Mounted Ductstat (Option AG3)
Figure 25. Remote Temperature Selector (Option AG15 or AG16)
OPTIONAL TWO-STAGE OPERATION—HEATING ONLY APPLICATION
The standard combination control valve is replaced with a two-stage combination gas control valve providing for
low fire or high fire operation controlled by a two-stage thermostat. The first stage (low fire) is factory-set (not field-
adjustable). Both low fire and high fire stages are controlled by a Servo regulator that maintains constant gas input
under wide variations in gas supply pressure. See the instructions provided with the unit for specific gas valve
specifications, wiring, and operating instructions.
OPTIONAL TWO-STAGE OPERATION—MAKEUP AIR APPLICATION
Two-stage makeup air units are equipped with a two-stage gas valve, but instead of control from a two-stage room
thermostat, the outlet air temperature is monitored and controlled by a two-stage ductstat. When discharge air
temperature drops to the setpoint, low fire is energized. If low fire cannot satisfy the ductstat setting, high fire is
energized.
Makeup air applications are usually adjusted to maintain discharge air temperature between 65°F and 75°F. In
all applications, the allowable temperature rise of the furnace in the installation dictates the limits of the ductstat
temperature setting.
Depending on the option selection, the factory-installed sensor is either field-connected by capillary tubing to the
unit-mounted ductstat (see Figure 24), which is factory-set at 70°F, or electrically-connected to a remote electronic
temperature selector (see Figure 25), which is available with or without a display module.
TEMPERAT URE-SELECTING MODULE
AGE ADDER MODULE
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