Automotive Air Conditioning. A Unique Variation…

Automotive air conditioning is really, one of a kind air conditioner type. It is also famously known as car air conditioners, although it's widely used in other road vehicles.

It uses the principle of gas compression and expansion to remove heat through the condenser, and take in heat through the evaporator.

If you ask me, I would say that automotive or car air conditioners are vital for travelling within an enclosed space.

Fossil fuel price will spiral up, and keep rising until who knows when. Hence, automobiles have to be designed with aerodynamically shaped body, and your windows have to be raised as well.

Otherwise, bye-bye fuel economy.

A car, being an insulated space, with large window areas, and metal body, is sure to be a good thermal conductor. A few minutes inside the car, under the sun will create a tremendous discomfort.

Likewise in cold weathers.

Hence, automotive air conditioning has to be fitted in almost, all cars.


Overview of automobile air conditioning:

I term automotive or car air conditioners as mini-central air conditioners, simply due to one reason.

It is fitted with ducts to supply air from the evaporator, to driver and passenger compartment.

Air conditioners for automobiles are designed such that, air can be directed straight to the occupants. As such, these are built mainly for spot cooling.

Why so?

Because heat gain through radiation is so quick in your vehicle that it will take a very long time before the whole space is conditioned, if it was designed for indirect cooling.

Heat loss during winter, however, is not that sudden, and hence indirect heating can be utilised.

I almost forgot to mention. Automobile air conditioning is sized about twice as large as room air conditioners.

All for the reason of large heat gain and loss through windows.


Design features:

Why the unusual list? Because those are unusual in nature, compared to fixed air conditioners. How so? Here comes…

The unusual

  • Let’s begin with automobile air conditioning compressor.

    Power input for fixed air conditioners is provided by electricity, but not for air conditioners in your vehicle.

    Power comes directly from the engine, through a belt, or chain.

    Well, if it is directly connected, then how to switch on and off the compressor?

    No. Switching on and off the engine is not an option. In fact the compressor is switched on and off through magnetic coupling and decoupling, as and when required.

    Most typical compressor type used in automotive air conditioners is the rotary type compressor.

    However, there is another compressor type that is unseen in room air conditioners.

    The swash plate type. These are essentially piston compressors, actuated by a swash plate

  • Suction throttle valve, or famously known as STV, is vital for proper operation of auto ACs.

    Suction throttle valves are connected to a vacuum switch, and located downstream of the evaporator.

    STV will open more, if a larger vacuum is detected at the switch, allowing for more refrigerant flow.

    When will the larger vacuum occur?

    When you press harder on accelerator pedal, and the engine (plus the compressor) rotates faster

  • Aluminium tubes are used in automotive air conditioning units for the light weight property, and cheap.

    Rubber hoses are coupled with aluminium tubes using hose clips. These are used to ease dismantling and reinstallation of the system in cramped space

  • Automotive air conditioners utilise a different control system for a variation of comfort setting.

    The difference lies in the air flow control.

    You can set to circulate most of the air within the cabin, or take in more fresh air.

    You can also set air flow within cabin to cool your face, feet, windshield (for indirect cooling), or a combination between those three settings.

    It is achieved by varying damper positioning

  • Why refrigerant is unusual in auto ACs? Because you’ll only find R-134a in these units


Others

  • Automotive air conditioning condensers are placed close to the front grille, for better cooling from moving vehicle. As such, the design can be a compact one.

    Evaporators are normally placed underneath the front driver and passenger dashboard

  • Dampers are normally controlled manually, through linkages, but modern vehicles have electrically controlled dampers

  • Digital control panels are a norm, with "AUTO" mode

  • Evaporator blowers are normally of variable speed one, used during "AUTO" mode for better comfort control

  • Automotive air conditioner parts are mainly constructed from cast iron (for compressor) and aluminium (for tubing)


Service and maintenance:

Maintenance list is similar to fixed air conditioners.

Additionally, you have to check on belt tension every 80,000 kilometres, together with timing belt change, or at interval suggested by your car manufacturer.

It is also good to check on rubber hose leakage every year.


Wrap up:

I hope that the information on automotive air conditioning had helped you in understanding the general philosophy of its design.

Why not drop me a feedback from the footer link should you need more clarification, or any other question on automotive air conditioning, or car air conditioners.



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