Honeywell Home explains that a flashing Cool On message normally indicates a built-in compressor protection delay.
What Cool On flashing means
Honeywell Home explains that a flashing Cool On message normally indicates a built-in compressor protection delay.
What you may notice
- The display or status light shows Cool On flashing
- Cool On, Heat On, a snowflake, or flame icon blinks
- The equipment does not start immediately
- A Wait message may appear
Most likely causes
- 01The compressor protection timer is active
- 02Power was recently restored
- 03The setpoint changed soon after shutdown
- 04Thermostat voltage is unstable
- 05The HVAC equipment is not responding
Safe checks, in order
Start with the simplest non-invasive check. Stop as soon as the error clears; repeated resets can hide a condition without correcting it.
Wait five minutes
The protective delay normally clears on its own.
Confirm the setpoint
For cooling set it below room temperature; for heating set it above room temperature.
Check basic system power
Confirm the HVAC breaker and service switch are on.
Stop if it keeps blinking
A delay that does not clear may require voltage and equipment checks.
Know where to stop
Do not bypass compressor protection or move thermostat wires while the HVAC circuit is energized.
When to call a technician or support
Call an HVAC professional if the blinking continues beyond the normal delay or the equipment never starts.
When you call, have the exact product model, the complete code or light pattern, and when it appeared.
Where this information came from
We use the manufacturer's current published guidance as the starting point, then organize it into a safer, beginner-friendly sequence.
Honeywell Home Support — thermostat delay messages Source last checked August 18, 2026. Manufacturer instructions and model manuals take priority over this independent summary.