The air-conditioning system

A decade ago, the air-conditioning (A/C) system was an extra feature in a vehicle just like the heated seats, a full airbag system, the reverse camera and sensors… However, nowadays it has become a necessity because of many aspects, such as the huge increase of cars on the roads causing loads of traffic jams and the amount of jobs requiring a long time driving in the hot weather.

The A/C system consists of numerous parts that differs between automotive brands:

• The compressor: Increases the pressure of the refrigerant in the system.
• The A/C hoses (High and low pressure): Connect all the system’s components to create a closed loop
• The condenser: Cools the refrigerant
• The fans: Blow cold air through the condenser
• The receiver dryer OR The accumulator: Removes the moister from the system
• The thermal expansion valve OR The orifice tube: Regulates the flow of the refrigerant in order to expand it and reduce its pressure.
• The evaporator: Absorbs the heat from the cabin to cool the refrigerant and turn it into gas (You might see ice forming on this component)
• The blower: Blows cold air from the evaporator into the cabin

Figure 1: Air-conditioning system diagram (Did It Myself, 2019)

The system works by changing the pressure of the refrigerant gas which affects its temperature, this pressure-temperature relation is similar to a sprayer can getting colder when spraying for a long period of time. According to Guy-Loussac’s law, pressure and temperature are proportional, hence a low-pressure gas has a low temperature (cold) whereas high pressure gas inflicts a high temperature (hot).

The air coming out of the vents has always the same temperature. The temperature set on the A/C panel (Marked in blue in figure 2) is the desired cabin temperature. Consequently, once the actual temperature of the vehicle’s cabin reaches the desired one, the A/C compressor shuts off.

The recirculation loop button (Indicated in red in figure 2)assure a closed loop air system by preventing any outer air (Mostly hot) coming into the cabin which allows the air-conditioning system to transform the hot air inside your cabin to cold air.
The A/C button switch (Circled in yellow in figure 2) turns on and off the compressor manually.

Figure 2: Air-conditioning panel

Although the manufacturers are developing more efficient A/C systems, it remains the most fuel consuming feature in a vehicle when turned on (an increase of up to 20%), and that’s due to the fact that the compressor’s pulley is rotated by the drive belt that is connected to the crankshaft pulley which adds load on the engine.

Nevertheless, it is possible to reduce this increase of fuel consumption, here some tips:

• Adjust your thermostat settings to a comfortable temperature rather than a cold one.
• Always use re-circulation to cool only the air inside the car
• Open the windows without any A/C at start-up (For few minutes)
• Park your vehicle in the shade or use window shades to reduce the heat inside the car

   References:

• Did It Myself. (2019). Recharging Car Air Conditioning - Did It Myself. [online] Available at: https://did-it-myself.com/recharging-car-air-conditioning/ 
• Completely Firestone. (2019). All About Your Car's A/C System | Firestone Complete Auto Care. [online] Available at: https://blog.firestonecompleteautocare.com/maintenance/everything-you-need-to-know-about-your-cars-ac/
• Nrcan.gc.ca. (2019). Vehicle air conditioning | Natural Resources Canada. [online] Available at: https://www.nrcan.gc.ca/energy/efficiency/energy-efficiency-transportation-and-alternative-fuels/choosing-right-vehicle/tips-buying-fuel-efficient-vehicle/factors-affect-fuel-efficiency/vehicle-air-conditioning/21030