Unit Start Up
RT-SVX36K-EN 153
If the measured carbon dioxide level is between 8.0%
and 9.5%, no adjustment is necessary. If the CO
2
is
outside this range, it indicates incomplete combustion
due to inadequate air or excessive gas.
The pressure ratio and bias adjustment screws are located
on top of the regulator under a sealed plate.The actual
settings can be seen through windows on each side of the
regulator. Refer to the illustration in Figure 122, p. 154.
Note: The burner capacity is controlled by the movement
of the air damper.This has been preset at the
factory and normally does not need field
adjustment.The combustion quality (air/gas) is
controlled by the settings on the regulator (the plus
(+) and minus (-) indications relate to the change in
gas flow.
7. Set the air/gas ratio to the desired value using the #1
adjustment screw until the optimum values between
(8.0 and 9.5%) are obtained (course setting).
8. Use Table 42, p. 96 to program the minimum (5%)
firing rate. Allow the system to operate for
approximately 10 minutes.
9. Use a carbon dioxide analyzer and measure the
percentage of carbon dioxide in the flue gas. 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
2
and in the
Minus (-) direction to decrease the CO
2
. Refer to the
illustration in Figure 121, p. 152 for the adjustment
screw location.
Note: It is normal for the low fire CO
2
to be lower than the
high fire.
10. If the measured carbon dioxide level is below the
recommended values for low heat, return the burner to
90% fire rate and repeat steps 6 and 7, to achieve
optimum combustion.
11. Program the burner for 100% operation and recheck
the CO
2
or O
2
value.
12. Check the flue gas values at several intermediate
output levels. If corrections are necessary;
– Adjust the pressure ratio screw 1 at high fire
operation only.
– Adjust the bias screw 2 at low fire operation only.
13. Press the STOP key at the Human Interface Module in
the unit control panel to stop the system operation.
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 DischargeTemperature
Control units. ZoneTemperature 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
Table 42, p. 96 to program the limited modulating heat
system components for 90% operation by scrolling
through the Human Interface displays.
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
combustion air damper is limited by a welded stop.
3. Press the STOP key at the Human Interface Module in
the unit control panel to stop the system operation.
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