@sunflowerinrain yes, AC is cooling only. It's usually integrated into HVAC (heating, ventilation, and air conditioning) systems. A single thermostat has a switch to toggle between heat (selected temperature is a lower limit) and cool (selected temperature is an upper limit) modes which turn on the heater and fan, or the air conditioner and fan.
My habit is to set it to 18C lower limit in winter and 27C upper limit in summer, because I'm comfortable anywhere in the range. But I know people who, because they want to be warm in winter and cool in summer, set the summer temperature colder than the winter one. I find that baffling.
@khird
Thanks! Clearer now.
Here we are more confusing, because the systems used for cooling and dehumidifying are called "chauffage" (heating) and are often run by heatpumps. They're just switched over, or "reversed" to cool indoors, so I've been putting the heating on during the heatwave.