Midco Unipower G-Series - Manual (Page 10)

Low Fire Adjustment:
2-Step Burners
Low Fire Adjustment:
Modulating or Optional
2-Step Burners
VII Initial Start -Up
Continued
1 4 . Check the draft control to make sure there is no spillage of flue products into the boiler room. This
test is should be performed under the most severe possible ventilating conditions. For example,
perform this test with all doors and windows tightly shut and any ventilating fans in the building
o p e r a t i n g .
1 5 . Start and stop the burner several times with the controller and the limit controls to check
their operation.
1 6 . Reset controller and limits controls to their desired settings. Replace wires and remove jumper on
Modulating or 2-Step burners.
* Refer to trouble chart.
With damper arm type motorized main automatic valves, see Figure 12.
1 . With the burner power off, remove jumper from terminals "3-4" of fluid power actuator, and
remove wire of the high/low controller from terminal 4 of the actuator. The actuator is factory set
to a maximum low fire input of 50% of the high fire setting. Check to make sure the low fire
adjustment cam (located in the lower left hand corner of the actuator wiring compartment) is set
at MAX.
2 . Lock blower shutter 1 / 2 open, start the burner and establish the main flame. Loosen the setscrew in
the cam with the special wrench taped to the inside of the actuator wiring compartment cover.
Keeping the wrench seated in the setscrew, rotate the cam slightly downward toward the base of
the actuator. Actuator will start to close.
3 . When the actuator reaches approximately the desired low fire position, quickly tighten the setscrew
and remove the wrench. Determine the gas input for the low fire setting by timing the meter gas
rate and reset blower shutter to achieve a stable flame as described in paragraph 11. Do not allow
input to fall below one-third of the high fire input rate or the recommended minimum input as
shown in Table 1, whichever is higher. If further adjustments are required, raise or lower the cam
and adjust the blower air shutter until a satisfactory flame is reached. Check combustion per
paragraph 13, page 9, and mark the position of the low fire shutter setting with a pencil or scratch
mark on the blower housing.
4 . Reconnect the blower air shutter connecting rod to the blower air shutter shaft. Turn burner off
and, operating linkages manually, adjust to index marked air shutter positions with high and low
positions of the main automatic valve. Cycle the burner several times with the on-off controller to
assure proper operation and correct linkage of the air shutter connecting rod. Conclude start-up
procedure per paragraph 14.
With motorized input adjuster, see Figure 13.
1 . Screw in low fire adjustment screw on
input adjuster as far as it will go. With
burner power off, transfer jumper from
terminals "R-B" to "R-W" and lock the
blower shutter about
1 / 2 o p e n .
2 . Start the burner and establish the main
burner flame. Back off the low fire
adjustment screw on the input adjuster
until the flame reaches the approximate
desired low fire position. Determine the
gas input for the low fire setting by timing
the meter gas rate and reset blower
shutter to achieve a stable flame as
described in paragraph 12. Do not allow
input to fall below one-third of the high
Figure 12: Damper Arm Type Motorized Main Automatic Valve Linkage
Figure 13: Motorized Input Adjuster Linkage