Midco J121A-3 - Manual (Page 6)

12. The actual NATURAL gas firing rate in BTU per hour
can be determined by timing the gas meter. Accurately
time the meter test dial for one revolution, convert to
hourly cubic feet and multiply by the BTU per cubic foot
value of your gas per formula:
Then divide by 1,000 for MBH value.
13. Start and stop the burner several times to check its
operation with the charging door open, and then with
it closed. Remove any temporary Door Open bypasses
installed in Step 6.
14. Test operation of any auxiliary operating and/or limit
controls.
15. Load incinerator and make trial run. Confirm that the
incineration chamber pressure stays within the range of
0 to minus 0.5"W.C. for Model J81A-3 and 0 to minus
1.0” W.C. for Model J121A-3.
16. WARNING: When the incinerator is located
inside a building and a draft control is used, check
that there is no spillage of flue products from the draft
control.
17. To shut off: Turn Burner Switch or Timer off and close
Main Manual Shut -Off Valve
PART 1 SERVICE
WARNING: BE SURE THAT THE MANUAL VALVE AND
BURNER DISCONNECT SWITCH ARE TURNED OFF BEFORE
ANY PARTS ARE REMOVED FOR SERVICE.
VIII IGNITOR AND REGULATOR ASSEMBLY
The Ignitor and Regulator Assembly is removed as a unit.
Disconnect the ignitor gas line and electrode wires, remove
the two mounting screws and pull out the assembly.
■ When the ignitor gas pressure is in the proper range (see
Table 4) and the electrodes are adjusted to the dimensions
shown in Figure 5, any ignition problems are usually
caused by lint, dust, corrosion, cracked electrode
insulators, foreign matter in the blast tube or deterioration of
ignitor ports in Retention Plate.
■ Ignitor trouble will be evidenced by failure of main burner
ignition. It may also be indicated by poor or erratic relay
response which cannot be remedied by ignitor gas
adjustment, or it may cause frequent Flame Safeguard
lockout. Check for dirt in the ignitor air and mixture
passageways and check for obstructions in the ignitor
ports. Also check electrode adjustments (see Figure 5).
Replace any severely burned parts.
■ Proper operation of the flame sensor rod can be checked
by measuring the flame signal. With the Flame Safeguard
energized and only the ignitor burning, a good reading
should run steady 2 or more volts DC.
■ When servicing, clean the Ignitor Retention Plate ports
and blow out the internal air and gas passages. Clean the
Electrode Insulators and check them for hairline cracks.
Also check the electrode ends and the Ground Barrier for
serious corrosion or loss of metal. Replace any defective
parts.
■ Make sure that there is no debris in the Blast Tube that
could short out the Spark or Flame Electrode.
■ Clean the Ignitor Gas Orifice in Tee Orifice Fitting (see
Figure 5) and check that the orifice size is correct per Table
4.
TABLE 4 Ignitor Firing Rate
Q7800 BASE FOR
RM7890 FLAME
SAFEGUARD
G
5
20
21
6
7
8
F
3
4
9
10
19
18
17
16
22
15
14
13 L2
12
L2 3 4 5 6 7 8 9 10 11
NEUTRAL
120/1/60
HOT
4 5
6
1
2
3
MAIN GAS VALVE
OPTIONAL
REDUNDANT VALVE
OPTIONAL VENT
VALVE
BLOWER MOTOR
NO
NC
C
SAFETY & OPERATING
CONTROLS
FLAME ROD
SPARK ROD
3 2 1
THERMAL
SWITCH
THERMAL SWITCH
OPTIONAL HI-LO GAS PRESSURE
SWITCH. IF USED, REMOVE
JUMPER 3-4
L2
L1
BK
3
10 Y 3 4
R/W
1 2
3
8
10
9
F
6
7
8
W(BK) IGNITOR GAS VALVE
BR BL BL
BL/W BK(W)
O
9
Y/BK BK
W
L2
6
HOT
120/1/60
NEUTRAL
SCHEMATIC
FUSED DISCONNECT
TERMINAL STRIP
SAFETY & OPERATING
CONTROLS
COMPONENT LAYOUT
Y/W
SWITCH OR TIMER
(LINE VOLTAGE)
(LINE VOLTAGE)
J81A-3 MOTOR END SWITCH
J121A-3 BLOWER AIR SWITCH
5
R
BL/W
Y/W
SPARK GENERATOR
R/BK
L2
L1
L
R/BK
IF NOT USED JUMPER
10 TO 3
FIGURE 2 Wiring Diagram
CAUTION: If a remote switch or timer is installed, remove or turn off the burner switch when using the remote control
TYPE
OF
GAS
NATURAL
PROPANE
NATURAL
PROPANE
IGNITOR
GAS
RATE
6 MBH
7 MBH
13 MBH
15 MBH
IGNITOR
ORIFICE
DIAMETER
.052 (#55 Dr.)
.042 (#58 Dr.)
.070 (# 50 Dr.)
.063 (#52 Dr.)
RECOMMENDED
IGNITOR GAS
PRESSURE
3.5 "W.C.
-6-
3600 x Test Dial Size x BTU Value
No. of Seconds for One Rev. Test Dial
= BTU/Hr.
Example: 3600 x 1 x 1000*
20
*Approximate BTU value.
=180,000 BTU/ Hr. = 180 MBH
MODEL
J81A-3
J121A-3