5-565.1
13
19. Recheck the gas supply pressure at the field installed
manual shut-off valve. The minumum inlet pressure should
be 6" W.C. on natural gas and 11" W.C. on propane gas.
The maximum inlet pressure for either gas is 14" W.C. If
inlet pressure exceeds 14" W.C., a gas pressure regulator
must be added upstream of the combination gas valve.
20. Open the field installed manual gas shut-off valve.
21. Open the manual main gas valve on the combination gas
valve. Call for heat with the thermostat and allow the pilot
to light for intermitent pilot ignition. If the pilot does not light,
purge the pilot line. If air purging is required, disconnect the
pilot line at outlet of pilot valve. In no case should line be
purged into heat exchanger. Check the pilot flame length
(See Pilot Flame Adjustment).
22. Once the pilot has been established, check to make sure
that the main gas valve opens. Check the manifold gas
pressure (See Main Gas Adjustment) and flame length (See
Air Shutter Adjustment) while the supply fan blower is
operating.
23. Check to insure that gas controls sequence properly (See
Control Operating Sequence). Verify if the unit has any
additional control devices and set according to the
instructions in the Control Options.
24. Once proper operation of the unit has been verified, remove
any jumper wires that were required for testing.
25. Close the electrical compartment door.
26. Replace all exterior panels.
Refer to page 54 for the Start-up Checklist.
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 13.1).
4. Replace the cap from the pilot adjustment screw.
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 or at the pressure tap of the gas valve for standard gas
string. (See Figure 14.1).
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. For
natural gas 3.5” W.C., for propane gas 10” W.C. 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 14.2 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.
unit installation / start-uP Procedure
figure 13.1 - correct Pilot flame
3/4" to 1"
