Summer is just around the corner and, especially for those of us lucky enough to reside in the Southern U.S., this can mean sweltering temperatures. Keeping your car, truck, van, or SUV cooling properly is going to get more and more difficult as spring gives way to those scorching days of summer. Now is the time to begin some basic maintenance on your climate control system, paying particularly close attention to that air conditioning unit and its complex components.
In this, the first of two parts, we will take a look at individual automotive air conditioning components. We will pay close attention to the two primary air conditioning designs being used in today’s automobiles and how these individual components function therein. In Part 2 we will concentrate on the operation of the automotive air conditioning system and why it is effective in cooling passenger compartments in the hottest of circumstances along with some basic annual maintenance on the a/c in your ride.
The air conditioning compressor is the heart of any air conditioning system. Think of it as the pump that moves both Freon and oil throughout the system. From one direction the compressor “sucks” a mixture of Freon and oil in and pumps it out in the opposite direction. We will discuss varying degrees of pressure in the second part of this free guide, but for the sake of understanding, you must know that the compressor draws Freon and oil in as a low pressure gas and discharges it as a high pressure gas.
Attached to the compressor is the suction/discharge manifold hose or hoses. Typically this will consist of an aluminum manifold with reinforced rubber hoses crimped onto it. Low pressure Freon gas is sucked into the compressor via the suction side of the manifold and high pressure gas is emitted from the discharge side. The rubber suction hose has an aluminum fitting crimped onto the end opposite the compressor which is affixed to either the evaporator core or the accumulator assembly, depending upon the design of the air conditioning system. The rubber portion of the discharge hose utilizes the same method of attachment, this time to the condenser. Specially made rubber O-rings are used to form an air (or intensely hot high-pressure Freon) tight seal between aluminum air conditioning components and a high-pressure crimping method is used to connect rubber hoses to aluminum fittings.
The condenser is often mistaken for the radiator, which is understandable because it is located in front of the radiator, it is approximately the same size as the radiator, and it uses fins for cooling just like the radiator. Extremely hot high-pressure Freon gas is pumped from the compressor, through the discharge hose and into the condenser. The condenser uses a finned design to capture airflow (created by ambient air when moving and electric fans when idling) across multiple aluminum tubes to effectively condense the Freon, transforming it from a high pressure gas into a very hot high-pressure liquid. Without this airflow the air conditioning system will not cool effectively and may even suffer catastrophic damage. The liquid Freon leaves the condenser and goes to the receiver dryer in one type of air conditioning system and directly to the expansion valve or fixed orifice tube in another. The line from which the Freon is pumped out of the condenser is called a liquid line.
The majority of vehicles imported into the U.S. are equipped with a receiver dryer in the liquid line between the condenser and the expansion valve, while domestic vehicles tend to use an accumulator in the low pressure gas hose instead. The receiver dryer acts to remove moisture from the system with multiple desiccant particle filters.
The expansion valve is located in the immediate vicinity of the evaporator core. As hot, high-pressure liquid Freon is pumped towards the evaporator core, the expansion valve uses a temperature sensitive capillary tube to control Freon flow through an integrated valve. The ability to control the flow of Freon is vital to the system’s ability to cool. As the flow is restricted the pressure of the Freon drops, turning it rapidly back into a low pressure gas, and it begins to boil. We will examine the scientific reason for transforming Freon from a high pressure liquid into a low pressure gas, and how it affects cooling, in Part 2 of this series.
The domestic system uses a fixed orifice tube which is inserted into the evaporator core, itself. Orifice tube size and design varies with different manufacturers but all are very similar. A small screen type housing contains a tube with a tiny opening that restricts Freon flow to the evaporator core. The screen is very fine and it captures debris and moisture from the liquid Freon as it is delayed by the restrictive opening in the tube. In a similar manner to the expansion valve, the orifice tube restricts Freon flow creating a rapid drop in pressure causing it to boil and fill the evaporator core simultaneously.
The evaporator core, as the name implies, serves to evaporate the Freon rapidly cooling it down using air created by the blower motor in the dash. The boiling Freon entering the evaporator core is pumped through small finned tubes similar to a miniature radiator. As the boiling low pressure Freon gas fills the evaporator core it emits a freezing vapor which the cooling fan blows from the vents of the dash. The cool air which blows from the vents is only one portion of the cooling process, be sure to check out the Blue Collar Blog for the Free Automotive Guide: Air Conditioning – Part 2 when we explain how Freon boils when it reaches the evaporator core, as well as other scientific parameters for keeping cool in the humid summer months to come.
Before low pressure Freon gas begins to settle in the evaporator core the compressor uses its suction to draw it out. On domestic cars and light trucks an accumulator is located very near the evaporator core in the suction hose (mentioned before in the suction discharge manifold). In this type of system the accumulator is used as a filter, as well as to remove moisture by using desiccant particles contained in one or more small bags. The Freon drops into the accumulator for filtering before being sucked back into the compressor, where the cycle begins anew.
You may have noticed that this whole process works in a circle; beginning with the compressor and ending with the compressor. Actually, ending when the engine or air conditioner are shut-off. If you did, then the chances of you grasping a good understanding of how an automotive air conditioning system works are very good. Be on the lookout for Free Automotive Guide: Air Conditioning – Part 2, when we will take a look at the science of automotive air conditioning and some helpful maintenance tips, as well.