Fault codes covered
19-06
The 27VPA models are capable of communicating with select thermostats that utilize Power Line Communication (PLC) for enhanced features. By default the OD unit does not display PLC communication faults in order to eliminate nuisance faults on systems that don’t have PLC capable thermostats. For systems installed with PLC capable thermostats, changing DIP switch #3 to HIGH will allow the OD unit to display any communication faults between the OD and the thermostat.
If communication between the OD unit and the PLC capable thermostat is lost for more than 2 minutes, enhanced control reverts to traditional 24VAC control and this fault code is set. The system will continue to run and satisfy cooling and heating demands with 24VAC controls. Once communication resumes between the OD unit and the thermostat, enhanced control will resume.
NOTE: If PLC communication is a persistent problem, the 24VAC control wiring can be shielded by use of Accessory EMI chokes. Refer to unit Product Data for compatible Accessory Choke Kits.
Source: ACHPVSR454-02SM troubleshooting pages.