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START-UP PROCEDURE
Main Burner Adjustment
The gas pressure regulator (integral to the combination gas
control) is adjusted at the factory for average gas conditions.
It is important that gas be supplied to the duct furnace in
accordance with the input rating on the serial plate. Actual
input should be checked and necessary adjustments made
after the duct furnace is installed. Over-firing, a result of too
high an input, reduces the life of the appliance and increases
maintenance. Under no circumstances should the input exceed
that shown on the serial plate.
Check/Adjust Pressure at the Combination Gas Valve
This section applies to all units, regardless of gas control type.
1.
Turn the field installed manual shut-off valve to "OFF".
2.
Remove the 1/8" pipe plug in the pipe tee or gas valve and
attach a U-tube type water manometer which is at least 12"
high and capable of reading to 0.1" W.C. See Figure 21.1.
3.
Turn the field installed manual gas shut-off valve to "ON".
Figure 21.1 - Checking Manifold Pressure with "U"
Tube Manometer
4.
Create a high fire call for heat from the thermostat.
5.
Determine the correct high fire manifold pressure, which
depends on gas type and gas control type. Review the
furnace Model Digit 11 and 12 (not the system model
number) and adjust the main gas pressure regulator spring
to achieve the proper manifold pressure as shown in Table
21.1. For location of regulator adjustment, refer to the
combination gas control literature supplied with the unit.
Table 21.1 - Manifold Gas Pressure - Main Valve
Furnace
Model Digit 11
N
(Natural)
P
(Propane)
j For units with Model Digit 12=9 and multiple furnaces, only one furnace
will be Model Digit 12=9, the additional furnaces will be Model Digit 12=2,
therefore pressures will be different for those furnaces.
6.
If the unit has Electronic Modulation gas controls (Model
Identification Digit 12=4, 7, 8, or 9), skip steps 7 through
9 in this section and proceed to the next section "Check/
Adjust Pressure for the Modulating Valve", otherwise
continue to the next step.
U-TUBE
MANOMETER
MANIFOLD
Furnace
Model Digit 12
Manifold Pressure
1, 2, 4, 7, 8
3.5"
4.0"
9 j
1, 2, 4, 7, 8
10.0"
9 j
10.5"
7.
After adjustment, move the field installed manual shut-off
valve to the "OFF" position, remove the manometer, and
replace the 1/8" pipe plug.
8.
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.
9.
Proceed to the section "Air Shutter Adjustment".
Check/Adjust Pressure for the Modulating Valve
This section only applies to units with Electronic Modulation gas
controls (Model Identification Digit 12=4, 7, 8, or 9). Refer to the
appropriate instructions for the valve type on the unit.
For Units with Model Digit 12=4, 7, or 8:
The low fire gas pressure needs to be adjusted. This needs to
be repeated on each furnace in multiple furnace units. Using
Figure 21.2 for item locations, this is accomplished as follows:
1.
Disconnect power.
2.
Remove all wires from Maxitrol Amplifier terminal "3" or duct
furnace terminal "43" (if available).
3.
Turn on power at the disconnect switch.
4.
Remove the maximum adjustment screw (4), spring (5),
and plunger (8). A small magnet is useful for this purpose.
CAUTION - The plunger is a precision part. Handle
carefully to avoid marring or picking up grease and dirt. Do
not lubricate.
5.
Using minimum adjusting screw (9), adjust low fire manifold
pressure to 0.56" W.C. for natural gas and 1.6" W.C. for
propane gas.
6.
Replace plunger and spring retainer, spring, and maximum
adjusting screw in proper order.
7.
Using maximum adjustment screw (4), adjust high fire
manifold pressure to 3.5" W.C. for natural gas and 10" W.C.
for propane gas.
TEE
8.
Disconnect power.
9.
Replace cover plate (2) and re-install all wires from Maxitrol
amplifier terminal "3" or duct furnace terminal "43".
10. After adjustment, move the field installed manual shut-off
valve to the "OFF" position and replace the 1/8" pipe plug.
(continued next page)
Figure 21.2 - Maxitrol Modulating Valve Adjustments
1
10
9
8
7
6
5-594.10
2
3
4
5
1.
TOP HOUSING
2.
COVER PLATE
3.
SEAL GASKET
4.
MAX ADJUSTMENT SCREW
5.
MAX ADJUSTMENT SPRING
6.
SOLENOID
7.
MIN ADJUSTMENT SPRING
8.
PLUNGER
9.
MIN ADJUSTMENT SCREW
10. MIN ADJUSTMENT SCREW STOP
21
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