Lennox SLP99UHV Series Unit Information page 68

J- Proper Ground and Voltage
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 52. 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
TABLE 33. If the readings exceed the maximum
shown in the table, make repairs before operating
the furnace.
CHECK VOLTAGE BETWEEN LINE NEUTRAL
AND LOW VOLTAGE "C" TERMINAL
DIAGNOSTIC LED
7-SEGMENT
2 - In addition, measure the AC voltage from Line Hot
to Line Neutral (spade terminals) on the integrated
control. See FIGURE 52. This voltage should be in
the range of 97 to 132 Vac.
Furnace Status
Power On Furnace Idle
CAI/Ignitor Energized
Indoor Blower Energized
CHECK VOLTAGE BETWEEN LINE HOT
HUM
EAC
W915
W951
W914
FIGURE 52
Page 68
TABLE 33
Measurement VAC
Expected
0.3
0.75
Less than 2
AND LINE NEUTRAL
7-SEGMENT
DIAGNOSTIC LED
Maximum
2
5
10
HUM
EAC
W915
W951
W914