Form RZ-NA I-SCE, Mfg #207697 Rev 4, Page 27
The gas train includes a single-stage gas valve, a modulating valve, and two gas pressure
switches. The burner rack is equipped with one flash carryover and a regulated gas lighter tube
system. The carryover lighter tube receives its gas supply through the regulator, simultaneously
with the gas to the burner. Control of the system is through a Maxitrol #ES410A amplifier with a
corresponding remote temperature dial (Maxitrol #ES410TD).
gu
gu
Carryover
Regulator
Modulating
Valve
Single-Stage
Gas Valve
P rimary Gas
Flow Pressure
Switch
White Label
1.1 w.c.
Gas Flow
Pressure Switch
White Label
1.1 w.c.
FIGURE 27 - Option
AG39 Manifold
Arrangement
Note: Arrangement may vary slightly
depending on gas valve; components
are the same.
Description of the
Operation of Option
AG39
The gas supply (see pressure requirements in the table above) connects to the single-stage gas
valve. To compensate for additional pressure loss through the modulating valve, the single-stage
gas valve has a custom outlet pressure setting higher than when it is used on a standard gas
manifold. The pilot tubing connects to the pilot port on the single-stage gas valve. When the
valve receives a call for heat from the amplifier and pilot is established, gas flow from the single-
stage valve goes to both the modulating valve and the regulated lighter tube system. When the
signal from the amplifier to the modulating valve requires less-than-high fire operation, the modu-
lating valve functions to lessen the gas flow to the burner to reduce the input rate to that required
to maintain the desired temperature. When the input rate is reduced enough to decrease the gas
pressure to 1.1" w.c., the primary gas pressure switch in the manifold activates the gear motor that
controls the bypass damper in the venter/combustion air system. The bypass damper opens
diverting some of the incoming air directly into the flue duct, reducing airflow through the burner.
Safety switches monitor the position of the bypass damper. When the gas pressure increases
above 1.1" w.c., the bypass damper closes.
Combustion Air
Pressure Switch
Settings for Model
SCE with Option
AG39 or AG40
Sensor Location
For the convenience of the installer, the duct temperature sensor is factory installed in the cabinet
leg (See
FIGURE 23
, page 25). Although the sensor has a mixing tube, at this distance from the
discharge it does not receive a true mix, so the temperature read by the sensor will be slightly
higher than the actual air entering the ductwork. The system will provide comfort level heat if the
selector is set slightly higher to compensate for this reading. If a direct correlation of these two
temperatures is required, move the duct sensor to a location in the ductwork about 10-12 feet (3-
3.7 M) from the furnace discharge.
Wiring and Service
For wiring, consult the wiring diagram attached to the furnace. All wires in the electrical box
connecting the modulation controls must have a temperature rating of 150°C.
This is a unique system which includes custom-built components and custom settings. If
service is required, follow the general troubleshooting guide on page 35 and the special trouble-
shooting guide in
FIGURE 28
.
This uniquely designed modulation system requires combustion air pressure settings different
from the standard system. The
Sizes with
Startup
Equilibrium
Factory
approximate settings for the
AG39&40
Cold
at Full Rate
Setting
combustion air proving switch
125-225
-1.3"w.c.±0.2
-1.05"w.c.±0.1
-1.0"w.c.±0.
0
2
250-300, 400 -1.2"w.c.±0.2 -0.95"w.c.±0.1 -.7
0
"w.c.±0.
0
5
at sea-level operation are:
21D. Computer Controlled Electronic
Modulation between 20-28% and
100% Firing Rate (U.S. Patent
6,109,255), Option AG40
- not available
on Size 350; available with natural gas only
With this option the furnace is equipped with a Maxitrol signal
conditioner (see illustration in
FIGURE 26
) which accepts an
input signal of either 4-20 milliamps or 0-10 volts from a cus-
tomer-supplied control device such as a computer. With the dip
switches on the conditioner in the "on" positions, the condi-
