In general, it is not cheaper to keep an empty home much cooler than necessary for hours. Reducing cooling demand while you are away usually saves energy, although the best strategy depends on climate, humidity, and the type of system.
An air conditioner does not work harder just because it has to recover
An air conditioner uses energy while removing heat. Allowing the home to warm a few degrees during an absence reduces the indoor-outdoor temperature difference and therefore the heat entering while you are away.
Avoid extreme shutdowns in humid climates
In very humid climates, shutting cooling off completely for many hours can let indoor humidity rise and affect comfort or materials. A higher setpoint rather than a full shutdown is often a better compromise.
Variable-capacity systems behave differently
Inverter and variable-capacity systems may run for long periods at low output without wasting energy. Judge performance by energy use and comfort rather than simply by how many hours the compressor can be heard.
Schedule a gradual recovery
A programmable thermostat can raise the setpoint when you leave and restore comfort before you return. If the system cannot reach setpoint even with clean filters and good airflow, the problem is capacity or service, not scheduling strategy.
Sources
- U.S. Department of Energy — Thermostats — Thermostat use, temperature setbacks, and heating and cooling energy savings.