Air conditioning is exactly what it says — conditioned air. It seems so simple but is widely misunderstood because most consumers associate AC with hot weather.
Removing heat from the air is the primary but not only role of an AC system. It also removes moisture from that air and in many ways that is the role that we notice and appreciate most. By removing moisture from the air, AC effectively makes it feel cooler. We’ve all heard the expression “it is a dry heat.” Most Canadians also know that a below-freezing day on the Prairies, away from water, is more pleasant than one at the exact same temperature in the Atlantic region, beside the ocean. The difference is the amount of moisture in the air — less is better.
Setting the AC System to 20, for example, means it will maintain that temperature, removing moisture in the process. Most systems are set to maintain 50-60 per cent moisture content. If the temperature goes above 20, the system will come to life and circulate the air, bringing it into the system where moisture is removed and, if necessary, heat removed to bring it down to the set temperature. It is then reintroduced to the room or vehicle interior.
That last sentence is where the misunderstanding lies. AC will remove heat if necessary to bring temperatures down to a set level. But if it is not necessary to lower the temperature, the AC system will simply remove moisture as necessary.
It will produce cold air if necessary to lower the temperature. It will not introduce “cold” air if the temperature is already at the set level.
There are two other AC-related issues I should cover at this point:
1. Automatic climate control. It is becoming increasingly common for automotive AC systems to maintain a set temperature automatically – cooling or heating the air as necessary. If the system is set for 20 and the temperature drops below that, the heater is used to bring the temperature up. If it rises above 20, the AC system will bring it down. The beauty of these systems is that they automatically control the moisture inside the vehicle, preventing the windows from fogging up in all but the most extreme conditions. Dual-zone systems allow occupants in either side of the front to set their own conditions. Tri- or three-zone systems allow a separate setting for seat occupants.
2. Windows open or close with the AC on? An open window will increase the drag as a vehicle moves through the air. The added drag increases in relation to speed. In any case, more power is needed, but the amount of extra power is minimal and the increase in fuel consumption in the one to three per cent range, depending on speed, vehicle design, ambient temperature, humidity levels and interior temperature.
