The EH error code on your 18k BTU ducted Chill Cube thermostat and ADB panel indicates a communication error between the thermostat and the air conditioning unit. To resolve this, first ensure all wiring and installation steps are correctly followed. If the error persists, contact Lippert Customer Technical Support for detailed troubleshooting assistance, as they have to diagnose and fix communication issues. They may and reconnecting the control board connectors or, if necessary, replacing the ADB panel, which can be defective. Having your model and serial numbers ready will facilitate support. If you need a replacement ADB panel or further help, Elkhart RV Parts can assist in coordinating with Lippert to get your unit running smoothly.