Midco J121-DS - Manual (Page 12)

12
Trouble Chart
C. Check for 24V* between strip terminals 6 to 10. No voltage, transformer is defective.
D. Check for 24V* between strip terminals 5 and10. No voltage, motor interlock switch is
defective.
E. Check for 24V* between Electronic Control 24 (PWR) terminal and strip terminal 10. 24V
yellow wire from strip terminal 10 is defective.
F. Check for 24V* between Electronic Control 24 (GND) terminal and strip terminal 10.
No voltage, red wire from terminal strip 5 is defective.
G. Turn burner control off for a minimum of 30 seconds to RESET Electronic Control for
each of the following steps.
CAUTION: Tests are valid only during the 6 second trial for ignition.
1. Check for 24V* between Electronic Control Valve terminal and strip terminal 10. No volt
age, Electronic Control or Fuse is defective.
2. Check for 24V* between strip terminals 7 and 10. No voltage, blue wire from strip
terminal 7 is defective.
3. Check for ignition spark (spark length approximately 1/8"):
a. Between Electronic Control HI VOLTAGE terminal and earth ground. No spark,
Electronic Control or Fuse is defective.
b. Between electrode wire and Spark Electrode. No Spark, Electrode wire is defective.
c. Check for spark between Spark Electrode and ground barrier. See Figure 5. If
ignitor tip is not visible with burner mounted, but spark can be heard, continue with
Step G4. If spark cannot be heard, refer to Section VIII IGNITOR AND REGULATOR
ASSEMBLY for spark test.
4. Connect manometer to Ignitor Gas Pressures Test Tap and, during 6 second trial for
ignition period, check gas pressure.
a. No pressure, confirm that pressure of at least 4" W.C. is available at inlet of
automatic gas valve (connect manometer to valve upstream tap) and repeat Step G4.
If still no ignitor gas pressure, valve is defective.
b. Ignitor gas pressure 3" to 4" W.C., continue with Step G5.
c. .Adjust the ignitor regulator to 3.5" W.C. while gas is flowing.
5. Open charging door, make sure any Door Open interlock is bypassed, and repeat trial
for ignition.
a. With flame on, close charging door and check combustion chamber pressure, burner
peep hole can be used for access to obtain approximate reading. Make sure sensing
tube extends into the combustion chamber for at 6". Pressure should be
between 0" and minus 0.5" W.C. If pressure is on the high negative side of the range,
increase the ignitor gas pressure to 4" or 5" W.C.
b. No flame, clean and test ignitor assembly per Section VIII IGNITOR AND REGULATOR
ASSEMBLY.
III FLAME ON ONLY DURING 6-SECOND TRIAL FOR IGNITION
A. With motor running check burner line voltage terminals for 120V as follows:
1. Between strip terminals L1 and L2 - 120V: voltage OK.
2. Between strip terminals L1 and GND.TERM - 120V: ground OK.
3. Between strip terminals L2 and GND.TERM. - no volt age: no back-feed neutral OK.
B. Follow test procedure as specified in Step II G.
1. Connect DC microamp meter in series with sense wire and Electronic Control SENSE
terminal. With flame on, flame signal should be steady and at least 2 microamps.
Check sense wire for continuity Adjust ignitor gas pressure to obtain acceptable
signal and note gas pressure and signal strength for future reference.
IV. SHORT FLAME
A. Low gas pressure
B. Air shutter open too far
C. Input adjuster not set properly
V. LONG HAZY FLAME
A. High gas pressure
B. Air shutter closed too far
C. Insufficient free air in combustion
chamber
D. Dirty blower wheel
E. Input adjuster not set properly
VI. GAS FAILS TO SHUT OFF
A. Defective automatic valve
B. High gas pressure
*Normal low voltage: Motor running - 24V minimum
Automatic valve energized - 21V minimum
Midco International Inc. 4140 West Victoria Street * Chicago, Illinois 60646
tel 773.604.8700 fax 773.604.4070 web www.midco-intl.com email [email protected]
602
8471 15
Printed in USA
Trouble Shooting
Continued