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Unit Start-up
pressure is within range shown in Chart B
124). If manifold pressure is not within the specified
range, contact Large Commercial Technical Support for
information on how to adjust maximum fan speed (FHi).
8. Use a flue analyzer to measure the oxygen (O
carbon dioxide (CO
), and carbon monoxide (CO)
2
levels in the flue gas. If the measured oxygen level is
between 3.0 to 5.0% and the carbon dioxide level is
between 8.5 to 10% and the CO is less than 100 PPM,
no adjustment is necessary. If an adjustment is needed,
check the inlet gas pressure or the air damper on the
burner (closing will increase the CO
110, p.
125.
Mid Fire Adjustment
9. Adjust the user interface to operate the furnace at mid
firing rate (approx. 38%).
10. Check the load line pressure on the ratio regulator.
Using the Modulating Gas Heat Actuator screen adjust
the % value until load line pressure is at 2" w.c.
11. Check manifold pressure at tap closest to where valve
train attaches to the burner. Refer to the illustration in
Figure 109, p.
125. Verify the manifold pressure is 0.8 -
0.9" w.c. If adjustment is necessary, turn the adjustment
screw on the ratio regulator. Refer to illustration in for
the adjustment screw location.
12. Program the burner for low fire operation (1%) and
recheck O
(or CO
) and CO values.
2
2
13. Press the STOP key on the user interface screen and
remove manual overrides to stop the system operation.
Table 60. Chart A - ultra modulating service mode
setup parameters
Modulating Gas
Heat Actuator
Low Fire
(Service Mode)
(1%)
VDC Signal to actuator
2.0 VDC
Inlet Pressure
7.0" to 14.0"
Main Gas Regulator
6.0"
Pressure - NG
Load Line Pressure -
NG
Manifold Pressure -
NG
Main Gas Regulator
10.0"
Pressure - LP
Load Line Pressure -
LP
Manifold Pressure - LP
Note: In the service mode, adjust the % output until the Load Line
Pressure is correct, then verify/ adjust manifold pressure.
124
(Table 61, p.
),
2
level). See
Figure
2
Mid Fire
(38%) (see
High Fire
note)
(100%)
5.0 VDC
10.0 VDC
7.0" to 14.0"
7.0" to 14.0"
6.0"
6.0"
2.0"
0.8" to 0.9"
See chart B
10.0"
10.0"
0.9"
0.12" to 0.17"
See chart B
Table 61. Chart B - high fire manifold pressure
High Fire Manifold Pressure
Burner size
NG
500 MBh
2.6" to 2.9"
850 MBh
1.6" to 1.9"
800 MBh
(a)
1.3" to 1.6"
1000 MBh
2.1" to 2.4"
Note: If the manifold pressure is not within the range shown on the chart,
then the maximum combustion fan speed (Fhi) needs
adjustment. Contact Large Commercial Technical Support for
assistance.
(a)
800 MBh is horizontal discharge. MBh is listed on gas heat rating plate.
Figure 106. Gas Heat Manual Override screen -
modulating
Figure 107. Ratio regulator— ultra modulating
Adjustment screw (under cap) for
manifold pressure adjustment during
low-fire and mid-fire pressure
adjustment only
LP
1.13"
0.65"
0.59"
0.91"
Tap location for
load line pressure
Connection for
combustion air line
RT-SVX072D-EN
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