How do I test AC-only mode on a heating and cooling system?
Answer
Set the thermostat to Cool or AC only, raise the setpoint below room temperature, and confirm the outdoor unit and indoor airflow start without unusual noises or error messages.
Before you start: stop right away if…
- Electrical and refrigerant repairs require a qualified technician.
Follow these steps
Select Cool or AC only
On the thermostat, choose Cool or AC-only mode rather than Heat, Auto, or Emergency Heat.
You should see: The thermostat shows Cool or AC mode.
Set a cooling demand
Lower the setpoint a few degrees below the current room temperature and wait a few minutes.
You should see: The system starts a cooling call.
Confirm outdoor unit and airflow
Check that the outdoor unit is running and that indoor vents are blowing air that becomes cooler over several minutes.
You should see: Cooling operation is confirmed, or one of those parts fails to start.
Note errors and next path
If AC only fails, write down any thermostat codes or unusual sounds and contact an HVAC technician with that information. If AC only works, the heating or mode-control side needs separate attention.
You should see: You know whether the problem is cooling-specific or elsewhere in the system.
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Extra tips
What to look for: Thermostat Cool or AC-only setting, outdoor unit starting, supply vents blowing cool air, and any error messages when switching modes
Before you change anything: Replace thermostat batteries if the display is weak. Know where the system breaker and outdoor disconnect are. Give the system several minutes after switching modes. Do not open electrical panels if you are not qualified.