Lennox ML193UH045P36B Unit Information page 15

Test 1
Check ignitor circuit for correct resistance.
Remove 4-pin plug from control.
Check ohms reading across terminals 2 and 4.
See table 7. If value is correct, this is the only test needed.
If the reading on the meter is not correct, (0 or infinity) then a
second test is needed.
Multi−Meter
(set to ohms)
Test 2
Check ignitor for correct resistance.
Seperate the 2-pin jack-plug near the manifold and check
resistance of ignitor at the plug. See table 7. If the reading
is correct, then the problem is with the wiring between the
jack-plug and the control. If reading is not correct, the
issue is the ignitor.
Multi−Meter
(set to ohms)
Test 3
Check ignitor for correct voltage
Insert meter probes into terminals 2 and 4 (use small
diameter probes in order not to damage plug).
Check voltage during 20 second ignitor warm up period.
See table 7. If voltage reads below these values, check for
correct supply voltage to furnace.
IGNITOR CHECKS
Test 1
Test 2
Multi−Meter
(set to VAC)
Test 3
FIGURE 11
Page 15
TABLE 7
Control Ohms
39 to 70
103085
24 to 47
100973
Integrated Control Detail
Integrated Control Detail
Integrated Control Detail
Voltage + 10%
120
95