What should I do when 'Cool On' or 'Heat On' is flashing on the display?
The flashing message means the built-in compressor protection feature is engaged. The thermostat is forcing the compressor to wait 5 minutes before restarting to prevent damage. Once the safe wait time has elapsed, the message will stop flashing and the compressor will turn on automatically. (Page 8)
From the official Honeywell TH3000 Programmable Thermostat manual, page 8
Have a follow-up question?
Answers from the official manual.
Common questions