Form I-XE/CRGB/RPB, Page 26
FIGURE 22 - Remote Temperature Selector, Stage-Adder
Module, and Optional Display Module for Ductstat in Two-
Stage Makeup Air Control Options
(Option AG15 or AG16)
24. Optional Mechanical Modulation
- Makeup Air Application
The mechanical modulation valve regulates the flow of gas to the main
burner, depending on the demands of the sensing bulb which is located
in the airstream adjacent to the heat exchanger. Inputs are varied from
50% through 100% of full rate in direct response to the modulating
control sensing element and depending on the temperature of outside
air being forced through the furnace. Outlet air or return air temperature
can be maintained within a range of 50°F to 100°F and is adjustable at
the mechanical modulating valve.
25. Optional Electronic Modulation
The type and capability of the electronic modulation system, depends
on the option selected. Electronic modulation options are identified by
a suffix to the Serial No. printed on the heater rating plate. AG7 is
identified as MV-1; AG8 is identified as MV-3; AG9 is identified as
MV-4; AG21 is identified as MV-A; AG39 is identified as MP-1; and
AG40 is identified as MP-2.
Installation NOTE
: Sizes 350 and 400 with electronic modulation
require a minimum of 6" w.c. natural gas supply pressure.
25A. Electronic Modulation between 50%
and 100% Firing Rate
(Options AG7, AG8,
AG9)
Depending on the heat requirements as established by the thermistor
sensor, the burner modulates between 100% and 50% firing. The ther-
mistor is a resistor that is temperature sensitive in that as the surround-
ing temperature changes, the Ohms resistance changes through the ther-
mistor. This change is monitored by the solid state control center (am-
plifier) which furnishes varying DC current to the modulating valve to
adjust the gas input.
Each modulating valve is basically a regulator with electrical means of
raising and lowering the discharge pressure. When no DC current is fed
to this device, it functions as a gas pressure regulator, supplying 3.5"
w.c. pressure to the main operating valve.
Refer to the wiring diagram supplied with the furnace for proper wiring
connections. Electronic modulation for heating controlled by a specially
designed room thermostat (60°-85°F) is identified as Option AG7. Elec-
tronic modulation control systems for makeup air applications con-
trolled by a duct sensor and temperature selector (55-90°F) are identi-
fied as either Option AG8 or Option AG9. The temperature selector
setting for Option AG8 is on the amplifier; Option AG9 has a remote
temperature selector. Both systems are available with an override ther-
mostat.
FIGURE 21 -
Ductstat
Control in
Option AG3
Sheetmetal
Retaining Plate Gasket
Sensor Capillary
Sensor Bracket
(NOTE:
Bracket may
not be the same as
the one illustrated
.)
1. Remove the access panel in the
ductwork adjacent to the 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.
FIGURE 23 -
Duct
Temperature
Sensor
Location
Adjustable range
0-120°F with a
fixed differential
of 2-1/2°F.
Temperature
Selector
Stage-Adder
Module
Optional
Display Module
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 (
FIG-
URE 21
) or electrically connected to a remote electronic temperature
selector (
FIGURE 22
). 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
ductstat illustrated in
FIGURE 21
is used with Option AG3. The con-
trol is set to 70°F and has an adjustable range 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.
23. Optional 2-Stage Operation -
Makeup Air Application (cont'd)
Optional Ductstat with Electronic Remote Setpoint Module (Op-
tions AG15 and AG16) -
The factory-installed sensing probe must be
field-wired to a remote temperature selector. The temperature selector
has an operating range to 120°F. The remote modules are shipped sepa-
rately 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 22
.
On outdoor models, mechanical modulation gas control is available with
bypass. With the bypass option, the unit is equipped with a single-
stage valve and relay. On call from a remote override thermostat, the
single-stage bypass valve cycles on at 100% fire.
Optional mechanical modulation control without bypass is identified as
Option AG6; mechanical modulation control with bypass is Option
AG13.
Specifications and operating instructions for mechanical modulating valve
may be found in control manufacturer's Specifications and Operating
Sheet in the instruction envelope accompanying the furnace. (See
FIG-
URE 23
for a general location of the factory-installed sensor.)
Installation NOTE:
Sizes 300, 350, and 400 with mechanical modula-
tion require a minimum of 7" w.c. natural gas supply pressure.
