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8. Use
9. Use a carbon dioxide analyzer and measure the percentage of carbon dioxide in the flue gas.
Note: It is normal for the low fire CO
10. If the measured carbon dioxide level is below the recommended values for low heat, return the
11. Program the burner for 100% operation and recheck the CO
12. Check the flue gas values at several intermediate output levels. If corrections are necessary;
13. Press the STOP key at the Human Interface Module in the unit control panel to stop the system
Limited Modulating Gas Furnace
Limited Modulating gas heaters are available for the 500, 850 and 1000 MBH heater sizes. These
heaters are available in the same cabinet sizes as the current heaters.
The firing rate of the unit can vary from 33% rated MBH up to the nameplate rating of the unit. The
turn down ratios, therefore, is limited to 3:1.
Heat Exchanger
The heat exchanger drum, tubes and front and rear headers utilities the same materials as the
standard two stage furnace.
Unit control
The unit is controlled by a supply air temperature sensor located in the supply air stream for
Discharge Temperature Control units. Zone Temperature Control units have two sensors, one
located in the supply air stream and the zone sensor. The temperature sensor signal is sent to the
Heat module of the IntelliPak Unit Control. The control signal from the Heat Module is an inverse
proportional 5 -10V DC. The higher the voltage signal, the lower the call for heat.
The 5 -10V DC. signal controls the angular position of the combustion air damper through a direct
coupled damper actuator motor. The position of the air damper in turn controls the combustion air
pressure that is sensed by the modulating gas valve. The greater the combustion air pressure, the
greater the call for gas and the higher the firing rate of the heater. As the temperature setpoint is
reached, the Modulating Heat control will cause the combustion air actuator to change the damper
position to a lower firing rate that matches the heat load of the space.
1. To verify and check system optimum combustion, use
2. Follow the checkout procedures discussed in the previous steps.
Note: The minimum firing rate for a limited modulating gas furnace in step 8 is 33%. Travel of the
RT-SVX36G-EN
Table 35, p. 108
to program the minimum (5%) firing rate. Allow the system to operate for
approximately 10 minutes.
If the measured carbon dioxide level is between 6.0% and 8.0%, no adjustment is necessary. If
an adjustment is needed, turn the #2 adjustment screw on the regulator in the Plus (+) direction
to increase the CO
and in the Minus (-) direction to decrease the CO
2
in
Figure 85, p. 159
for the adjustment screw location.
burner to 90% fire rate and repeat steps 6 and 7, to achieve optimum combustion.
– Adjust the pressure ratio screw 1 at high fire operation only.
– Adjust the bias screw 2 at low fire operation only.
operation.
modulating heat system components for 90% operation by scrolling through the Human
Interface displays.
combustion air damper is limited by a welded stop.
to be lower than the high fire.
2
Table 35, p. 108
Unit Start Up
. Refer to the illustration
2
or O
value.
2
2
to program the limited
161
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