Reznor SCE Unit Installation Manual - Manual (Page 25)

Form RZ-NA I-SCE, Mfg #207697 Rev 7, Page 25
18. Operating
Valve
All furnaces are equipped with a 24-volt combination valve which includes the automatic electric
on-off valve controlled by the room thermostat, the pressure regulator, the safety pilot valve, and
the manual shutoff valve. The standard gas valve allows for single-stage control from a single-
stage, 24-volt thermostat.
WARNING: The operating valve is the prime safety shutoff. All gas supply
lines must be free of dirt or scale before connecting the unit to ensure positive
closure. See Hazard Levels, page 2.
19. Optional 2-
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. First stage
(low fire) is factory set (not field adjustable). Both high and low stages are controlled by a Servo
regulator, maintaining constant gas input under wide variations in gas supply pressure. See
instructions packed with the unit for specific gas valve specifications, wiring, and operating
instructions.
20. Optional 2-
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 the 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 discharge an outlet 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 (FIGURE 24) or electrically connected to a remote
electronic temperature selector ( FIGURE 25). The remote temperature selector is available with or
without a display module.
See FIGURE 23 for a general location of the factory-installed sensor with either the factory-
mounted or the remote ductstat selector option.
Optional Ductstat with Capillary Tubing (Option AG3) -- The control illustrated in FIGURE 24
has an adjustable range from 0° to 100°F with a fixed differential of 2-1/2°F. Due to different CFM
settings and outside air temperatures, the average downstream outlet temperature may not match
the ductstat setting exactly. After the installation is complete, adjust the setpoint of the ductstat
to achieve the desired average outlet air temperature.
Optional Ductstat with Electronic Remote Setpoint Module (Options AG15 and AG16) --
The
field-installed sensing probe is field-wired to a remote temperature selector with a temperature
operating range to 130°F. The remote modules and sensing probe are shipped separately for field
installation. Follow the wiring diagram with the unit and the manufacturer's instructions for wiring
and installation. CAUTION: Be sure heat/cool selector switch is set at "Heat" position. There will
be one module for selecting temperature and one-stage adder module. The digital display module
is optional. See FIGURE 25 .
FIGURE 23 - Duct
Temperature Sensor
Location
FIGURE 24 - Ductstat
Control in Options AG3
Factory
set at
70°F
1. Remove access panel in ductwork
adjacent to control compartment
access panel.
2. Element is retained by spring clips.
3. Round gasket and metal retaining
plate provide airtight seal for capillary
and must be removed to remove the
element.