The air conditioning in winter

To prevent this, all the air conditioning systems are equipped with sensors that switch off the compressor when the outside temperature drops just above zero (usually already around 5°C), irrespective of the position of the control switch. If it is very cold, the only way not to fog up the windows is to send plenty of warm air towards the windscreen or to use the recirculation function for a very short while.

It must be said that, while for automatic A/C systems, it is enough to set the desired temperature and let the electronics do all the work, for manual ones – after parking for a long time in freezing conditions – it is advisable to set the temperature to maximum and wait a few moments before operating the fan. This will give the engine a chance to warm the coolant up a little because the fluid is also circulated in the radiator of the air conditioning system. At this point, you can switch the recirculation on so that the system can heat faster by working on the same air. However, the recirculation must be switched off if the windows start misting up.

Returning to automatic A/C systems, remember that they do not start the fan immediately at maximum speed as soon as the car is started to avoid hitting the passengers with an annoying jet of air. This logic is both intentional and useful when the engine is cold, and the heating is not working yet. The fan speed increases automatically after a short while (that varies considerably from model to model) when the air temperature is closer to the user's request.

One the consequences of this is that, after starting the engine, it is useless (if not counter-productive) to set the temperature to maximum, hoping to reach the desired temperature faster. Recirculation, which prevents – in whole or in part – the inflow of outside air into the passenger compartment, in winter it is useful to switch it on when you set off as long as the windows do not mist up.

Another key concept is that a more efficient engine, i.e. one that is more capable of transforming a large part of the energy contained in the fuel into mechanical power, dissipates less heat into the liquid of the cooling system. As this liquid is also used to transfer heat to the passenger compartment heating system, it implies that higher-efficiency engines (such as modern diesel engines) can decrease passenger comfort in the winter season because they cannot warm up the passenger compartment fast enough. Diesel engines with direct injection are much more efficient than petrol and diesel engines with pre-chamber, and therefore the air-conditioning system is often equipped with an auxiliary heater, usually electrically operated. Consequently, heating causes increased fuel consumption, like using the air conditioning for cooling in summer.

This is even truer for electric vehicles and plug-in hybrids. The former vehicles do not have a heat engine, while the latter can temporarily do without one and, therefore, the heating of these cars is always based on electric systems that have a significant impact on the range offered by the batteries. For this reason, it is useful to take advantage of the pre-heating function that many models offer when they are plugged into the mains to charge the batteries. In this way, once the car is on the move, the heating of the car will simply maintain the temperature previously reached, with considerably less energy consumption.