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START-UP PROCEDURE
Pilot Burner Adjustment
The pilot burner is orificed to burn properly with an inlet pressure
of 6-7" W.C. on natural gas and 11-14" W.C. on propane gas, but
final adjustment must be made after installation. If the pilot flame
is too long or large, it is possible that it may cause soot and/or
impinge on the heat exchanger causing failure. If the pilot flame
is shorter than shown, it may cause poor ignition and result in
the controls not opening the combination gas control. A short
flame can be caused by a dirty pilot orifice. Pilot flame condition
should be observed periodically to assure trouble-free operation.
To Adjust the Pilot Flame
1. Create a call for heat from the thermostat.
2. Remove the cap from the pilot adjustment screw. For location,
see the combination gas control literature supplied with unit.
3. Adjust the pilot length by turning the screw in or out to achieve
a soft steady flame 3/4" to 1" long and encompassing 3/8"-
1/2" of the tip of the thermocouple or flame sensing rod (See
Figure 11.1).
4. Replace the cap from the pilot adjustment screw.
Figure 11.1 - Correct Pilot Flame
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.
Measuring the manifold pressure is done at the tee in the
manifold for premium gas controls (Digit 13=0, 1, 2, or 3) or
at the pressure tap on the gas valve for standard gas controls
(Digit 13=4). (See Figure 11.2).
Figure 11.2 - Manifold Pressure Test Points
3/4" to 1"
Applies to all models.
5-564.4
To Adjust the Manifold Pressure
1. Move the field installed manual shut-off valve to the "OFF"
position.
2. Remove the 1/8" pipe plug in the pipe tee or gas valve and
attach a water manometer of "U" tube type which is at least
12" high.
3. Move the field installed manual gas shut-off valve to the
"ON" position.
4. Create a high fire call for heat from the thermostat.
5. Determine the correct high fire manifold pressure (3.5" W.C.
for natural gas, 10" W.C. for propane gas). (Pressures at
0-2,000' elevation are 3.5" W.C. for natural gas, 10" W.C.
for propane gas, for elevations above 2,000' refer to the
instructions in "Gas Connections - High Altitude Accessory
Kit" on page 9). Adjust the main gas pressure regulator
spring to achieve the proper manifold pressure (for location,
see the combination gas control literature supplied with unit).
6. If the unit has Electronic Modulation gas controls (determine
from the Model Identification Digit 12), the low fire gas
pressure needs to be adjusted. Using Figure 11.3 for item
number locations, this is accomplished as follows:
a. Disconnect power.
b. Remove all wires from Maxitrol Amplifier terminal "3" or
duct furnace terminal "43" (if available).
c. Turn on power at the disconnect switch.
d. 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.
e. 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.
f. Replace plunger and spring retainer, spring, and
maximum adjusting screw in proper order.
g. 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.
h. Disconnect power.
i. Replace cover plate (2) and re-install all wires from
Maxitrol amplifier terminal "3" or duct furnace terminal "43".
7. After adjustment, move the field installed manual shut-off
valve to the "OFF" position 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.
Figure 11.3 - Maxitrol Modulating Valve Adjustments
2
3
1
10
9
8
7
6
4
5
1. TOP HOUSING
2. COVER PLATE
3. SEAL GASKET
4. MAXIMUM ADJUSTMENT SCREW
5. MAXIMUM ADJUSTMENT SPRING
6. SOLENOID
7. MINIMUM ADJUSTMENT SPRING
8. PLUNGER
9. MINIMUM ADJUSTMENT SCREW
10. MINIMUM ADJUSTMENT SCREW STOP
11
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