Midco J121-DS - Manual (Page 9)

SPARK TEST—Main Manual Shut-Off Valve must be off. Place the Ignitor
Assembly on top of the burner with the electrode ends visible and good metal to
metal contact between the Ignitor Mounting Plate and the burner chassis.
Connect the high voltage wire to the spark electrode. Spark should be visible
during 6-second trial for ignition period and arc from the electrode end to the
Ground Barrier. It should be audible and visible, though it is rather thin and difficult
to see in bright light.
CAUTION: Circuit has 30,000 volt open circuit potential.
If the spark is not audible or visible it is leaking directly to ground. Before
removing electrodes, check to make sure voltage is available by positioning the
spark wire 1/8" from the end of the electrode.
Disconnect Flame Electrode wire and switch the high voltage wire to the flame
electrode and repeat test for insulator leakage.
CAUTION: Do not indiscriminately change the ignitor gas orifice size as
ignition troubles are rarely cured in this manner. The ignitor utilizes a
premixed gas/air mixture and, as the air input is relatively fixed, any
adjustment to the gas/air ratio that might be required for a specific
application should be made by careful adjustment of the ignitor regulator to
vary its outlet gas pressure. Pressure adjustments must be made when the
gas is flowing. If cleaning and electrode adjustment does not eliminate an
ignition problem, further checks are required. Refer to Trouble Chart.
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The ignitor assembly as shipped is pre-set during factory fire-testing and normally
needs no adjustment except in installations where the air shutter is full open. The
ignitor should not be adjusted until it is confirmed that good light-offs are not
possible with ignitor gas pressure adjustments only as described in Section VIII.
The Air adjustment screw is located under a plug button in the Ignitor Block about
1/2" behind the Ignitor Orifice (refer to Figure 5). A 5/64 (.078) inch hexagon wrench
is required for adjustment. Pry up the plug button to expose air adjustment screw.
Adjust the screw up or down to find the best Flame Signal or until repeatable and
stable light-offs are achieved. Ignitor airflow is decreased as the screw is turned
clockwise, and increased as it is turned counter-clockwise. Generally 3 to 5 turns up
from full closed (screw bottomed out) works best.
When adjustments are completed, replace plug button to protect adjustment
screw.
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The valve is a single function on-off type with automatic closing on current failure.
Replace entire valve if valve fails to open when power is applied or if leakage is
defected on standby.
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Model J121DS is equipped with 1/6 HP split phase 3450 RPM motor. It may contain
either a manual or auto-reset overload protector. It has no interlock, this function
being performed by an Air Pressure Switch on the burner. The motor features per-
manently lubricated ball bearings that require no routine oiling maintenance.
9
Consumer Instructions
Part 2
Service
Continued
TABLE 3 Ignitor Firing Rate
.070 ( #50 DR )
.063 ( #52 DR ) 3.5" W.C.
3.5" W.C. 13 MBH
15 MBH
TYPE OF
GAS
Natural
Propane
IGNITOR
ORIFICE DIA.
RECOMMENDED IGNI-
TOR GAS PRESSURE
IGNITOR
GAS RATE
VIII Ignitor Gas/Air
Adjustment
X Main Automatic Valve
XI Blower Assembly