Lennox EL297DFV Series Unit Information page 34

Troubleshooting Motor Windings
Ensure that motor windings are not damaged by perform-
ing the following tests:
NOTE - If your ohm meter is not an auto-ranging type, set
it to the highest ohm scale (100k ohms or greater) before
performing tests.
TABLE 12
Ohm Meter Range
Scale
in words
2M two megohm -- two million
ohms
200K two hundred kilohm -- two
hundred thousand ohms
20K twenty kilohm -- twenty
thousand ohms
2K two kilohm -- two thousand
ohms
200 two hundred ohm
FIGURE 11
Measure the resistance between each of the three motor
leads (3-pin plug) and the unpainted part of the end shield.
If the winding resistance to ground is <100k ohms, re-
place the motor and control module. If the resistance
to ground is >100k, the motor windings are fine. Pro-
ceed to Test B.
FIGURE 12
Measurement Range
ohms
0-2,000,000
0-200,000
0-20,000
0-2,000
0-200
TEST A
Test A
Use an ohmmeter to measure the motor phase-to-phase
resistance by checking these combinations of the the 3-pin
motor plug. For the purpose of this test, start at either end
of the connector as lead 1.
1 - The lead-to-lead resistance across any two leads
should be less than 20 ohms.
2 - Each lead-to-lead resistance should be the same. If
the measured resistance is greater than 20 ohms,
replace the motor and control module.
C- Heating Components
1. Ignitor
The SureLight ignitor is made of durable silicon nitride.
®
Longevity is enhanced by controlling voltage to the ignitor.
The integrated control provides a regulated 120 volts to
the ignitor for a consistent ignition and long ignitor life.
Ohm value should be 39 to 70. See FIGURE 14 for ignitor
location and FIGURE 15 for ignitor check out.
NOTE - The EL297UHV(X) furnace contains electronic
components that are polarity sensitive. Make sure that the
furnace is wired correctly and is properly grounded.
2. Flame Sensor
A flame sensor is located on the left side of the burner
support. See FIGURE 14. The sensor tip protrudes into
the flame envelope of the left-most burner. The sensor
can be removed for service without removing any part of
the burners. During operation, flame is sensed by current
passed through the flame and sensing electrode. The
SureLight control allows the gas valve to remain open as
long as flame signal is sensed. To check flame sense sig-
nal use the push-button found on the integrated control
and go to Field Test Mode. The menu will display the flame
signal. See TABLE 13 for flame signal.
Flame Signal in Microamps
Normal
2.6 or greater
Page 34
TEST B
Test B
FIGURE 13
TABLE 13
Low Drop Out
2.5 or less 1.1