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.

Miswired Module Troubleshooting

Table 12

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Lennox International Inc 4HP18LT manual Thermostat Demand Wiring, Miswired Module Codes