Lennox International Inc. 4HP18LT - Manual (Page 22)

506470-01 Issue 1007
Thermostat Demand Wiring
The diagnostic module requires a thermostat demand signal
to operate properly. The thermostat demand signal input,
labeled Y on the module, should always be connected to
the compressor contactor coil so that when the coil is
energized, the demand signal input is 24VAC. When the
coil is not energized, the demand signal input should be less
than 0.5VAC. Miswired Module Codes
Depending on the system configuration, some ALERT flash
codes may not be active. The presence of safety switches
affects how the system alerts are displayed by the module.
Miswiring the diagnostic nodule will cause false LED codes.
Table 12 Describes LED operation when the module is
miswired and what troubleshooting action is required to
correct the problem.
Page 22
Miswired Module Troubleshooting
Table 12