Why is 'Cool On' or 'Heat On' flashing on my display?
The flashing 'Cool On' or 'Heat On' message indicates that the compressor protection feature is engaged. This is a safety feature that prevents damage to the compressor by forcing it to wait a few minutes before restarting after shutdown. Wait 5 minutes for the system to restart safely without damaging the compressor.
From the official Honeywell Focuspro TH5220D Thermostat manual, page 3
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