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START-UP PROCEDURE
Check/Adjust Pressure for the Modulating Valve
(continued)
11. After the plug is in place, move the field installed manual
shut-off valve to the "ON" position and recheck pipe plugs
for gas leaks with soap solution.
12. Proceed to the section "Air Shutter Adjustment".
For Units with Model Digit 12=9:
The high fire gas pressure needs to be adjusted first, followed
by the low gas pressure. For multiple furnace units, this is only
required on the duct furnace that has the modulating valve
(Model Digit 12=9). This is accomplished as follows:
1.
Verify the main valve (valve before the modulating valve)
outlet pressure has been set to 4.0" W.C. for natural gas
or 10.5" W.C. for propane gas per instructions and Table
21.1 on the previous page. For multiple furnace units, the
furnaces without the modulating valves are to remain at 3.5"
W.C. for natural gas or 10.0" W.C. for propane gas. For
location of regulator adjustment, refer to the combination
gas control literature supplied with the unit.
2.
The Maxitrol EXA modulating valve series has a cover
secured with two screws that must be removed. Once
removed, there are a bank of (3) DIP switches and two
buttons and a communication LED for the user interface as
shown in Figure 22.1.
3.
Verify that the DIP switches are properly set to the "OFF"
position for switches 1 and 3 and "ON" for switch 2.
4.
Adjust the High Fire Setting as follows:
a.
Enable the unit controls and create a call for heat.
b.
Press and hold Button #1 on the modulating valve until
the LED lights solid red, then release.
c.
With the valve now in the high fire setting mode,
confirm or adjust the high fire manifold pressure to be
3.5" W.C. If the pressure needs to be adjusted, press
or hold Button #1 to increase gas flow and press or
hold Button #2 to decrease gas flow.
d.
If 3.5" W.C. cannot be attained, recheck the inlet gas
pressure as described previously. After addressing
any issues, if 3.5" W.C. still cannot be attained, step
the valve closed using button #2 to the point where
manifold pressure begins to be impacted. If the
pressure at that point is less than 3.3" W.C., recheck
your inlet pressure with the unit operating and adjust
as required.
e.
Save the setting by simultaneously holding Buttons
#1 and #2 until the LED turns OFF. If this is not
performed within 5 minutes, the control will default
to the previously saved settings and return to normal
operating mode.
4.
Adjust the Low Fire Setting as follows:
a.
Press and hold Button #2 on the modulating valve until
the LED light blinks red, then release.
b.
With the valve now in the low fire setting mode, confirm
or adjust the low fire manifold pressure to be no less
than the minimum shown on the furnace serial plate
in the box called "Min. Manifold Pressure". If the
pressure needs to be adjusted:
c.
Press or hold Button #1 to increase gas flow and #2 to
decrease gas flow. It is best to push and release button
#2 to single step the valve to the minimum manifold
pressure. Holding the button is likely to cause the valve
to close too far and lose flame.
22
d.
Save the setting by simultaneously holding Buttons
#1 and #2 until the LED turns OFF. If this is not
performed within 5 minutes, the control will default
to the previously saved settings and return to normal
operating mode.
5.
Once the setting of the modulating valve has been
completed, replace the valve cover removed earlier.
6.
Move the field installed manual shut-off valve to the "OFF"
position, remove the manometer, and replace the 1/8" pipe
plug.
7.
After the plug is in place, move the field installed manual
shut-off valve to the "ON" position and recheck the pipe
plug for gas leaks with soap solution.
8.
Proceed to the section "Air Shutter Adjustment".
Figure 22.1 - Maxitrol EXA Modulating Valve
SUPPLY POWER TERMINALS
CONTROL SIGNAL TERMINALS
POSITION FEEDBACK
WIRING TERMINALS
DIP SWITCHES
(1="OFF", 2="ON", 3="OFF")
LED INDICATOR
Air Shutter Adjustment
Proper operation provides a soft blue flame with a well-defined
inner core. A lack of primary air will reveal soft yellow-tipped
flames. Excess primary air produces short, well-defined flames
with a tendency to lift off the burner ports. For both natural
and propane gas, the air shutters can be adjusted to control
the burner flame height. The air shutters can be accessed by
reaching behind the manifold tee in Figure 21.1. The larger
models may require the removal of the manifold (see Manifold
Assembly Removal).
Adjusting the primary combustion air is achieved by resetting
the primary air shutters (See Figure 51.2). Prior to flame
adjustment, operate duct furnace for about fifteen minutes. The
main burner flame can be viewed after loosening and pushing
aside the gas designation disc on the side of the burner box.
1. To increase primary air, loosen the air shutter set screws and
move the air shutters closer to the manifold until the yellow
tipped flames disappear and a clean blue flame with a well
defined inner cone appears.
2. To decrease primary air, move the air shutters away from the
manifolds until flames no longer lift from burner ports, but
being careful not to cause yellow tipping.
3. Re-tighten set screws after adjustment.
5-594.10
BUTTON #2
BUTTON #1
1
2
3
4
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