Lennox ML193UHE Series Unit Information page 44

G- Proper Ground and Voltage
WARNING
Electric Shock Hazard. Can cause injury
or death. Unit must be properly grounded
in accordance with national and local
codes.
A poorly grounded furnace can contribute to premature
ignitor failure. Use the following procedure to check for
ground and voltage to the integrated control.
1 - Measure the AC voltage between Line Neutral
(spade terminals) and "C" terminal (low voltage
terminal block) on the integrated control. See
FIGURE 57. A wide variation in the voltage between
Line Neutral and "C" as a function of load indicates a
poor or partial ground. Compare the readings to the
table below. If the readings exceed the maximum
shown in TABLE 21, make repairs before operating
the furnace.
CHECK VOLTAGE BETWEEN LINE NEUTRAL
AND LOW VOLTAGE "C" TERMINAL
Red LED
Recall
2 - In addition, measure the AC voltage from Line Hot
to Line Neutral (spade terminals) on the integrated
control. See figure 57. This voltage should be in the
range of 97 to 132 Vac
Note - FIGURE 57 is a typical ignition control
illustration.
Furnace Status
Power On Furnace Idle
CAI / Ignitor Energized
Indoor Blower Energized
CHECK VOLTAGE BETWEEN LINE HOT
AND LINE NEUTRAL
Red LED
Recall
FIGURE 57
Page 44
TABLE 21
Measurement VAC
Expected Maximum
0.3
0.75
Less than 2
2
5
10