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1: How Automotive Air Conditioning works

how automotive air conditioning works

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<h1>How Automotive Air Conditioning works</h1><br><br>
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<h3>Thermal Expansion Valve:</h3>
<p style="text-align: justify">Another pressure-regulating device is the expansion valve. This is used by most import and aftermarket systems. The expansion valve can sense the pressure and temperature of the refrigerant, which makes it very efficient in controlling refrigerant to the evaporator. There are several different varieties of expansion valves. The most common type is the Chrysler "H" block valve and is quite efficient. The down side is that, like the orifice tube, it can become clogged with debris and have they contain moving parts which can stick or fail over time. An important thing to note is that by design the compressor can way out pump the flow of refrigerant through the expansion valve. This is why there is low-pressure from the expansion valve back to the compressor.</p>
<p style="text-align: justify">The expansion valve has a capillary tube with a thermal bulb that controls how far open or closed it is. The thermal bulb and the internal pressure of the refrigerant balance to control just the exact amount of refrigerant needed. The thermal bulb is clamped to the output of the evaporator. If not enough refrigerant is flowing to cool the evaporator this bulb will sense it and open more or vice versa.</p>
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<p style="text-align: justify">The receiver-drier is placed on the high side of expansion valve systems. Since this type of valve needs liquid refrigerant to function a receiver is used to ensure that the valve gets the liquid it needs.</p>
<p>The Receiver/Filter/Drier provides three functions:</p>
<ol>
    <li>It is a tank that holds excess refrigerant and the refrigerant that leaves it usually goes up a pickup tube and past a sight glass. Under normal operating conditions, vapor bubbles should not be visible in the sight glass.</li>
    <li>It has a filter in it to remove small amounts of debris from the system.</li>
    <li>It has a chemical in it that treats the refrigerant by removing moisture and acid.</li>
</ol>
<p style="text-align: justify">There are different types of receiver-driers and different desiccant materials used in them. Some of these desiccants are not compatible with R-134a and receiver-driers will be marked for use with either R-12 or R-134a. Newer type receiver-driers use a special desiccant that is compatible with both refrigerants. R-134a requires a different desiccant (XH7) in the accumulator or receiver/drier because the molecules are smaller than R-12 and quickly fill up the "holes" that absorb moisture in XH5 desiccant. This can lead to acid formation and sludging as well as desiccant breakdown in some applications. It is a good idea to replace the receiver-drier each time the system is opened for repair or anytime moisture and/or debris is of concern.</p>
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<p style="text-align: justify">Orifice type systems use an accumulator that is connected directly to the evaporator outlet and stores excess liquid refrigerant. Since liquid refrigerant going into a compressor can do serious damage to the compressor, the main purpose of the accumulator is to isolate the compressor from any damaging liquid refrigerant. Accumulators, like receiver-driers, also remove debris and moisture from a system. It is also a good idea to replace the accumulator each time the system is opened for repair or anytime moisture and/or debris is of concern.</p>
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<p style="text-align: justify">The reason vehicle manufacturers choose R-134a to replace R-12 is because R134a comes closer to the cooling properties of R-12 than any other alternate refrigerant. Even R-134a is so close to R-12; it is not a direct replacement. They are chemically different and incompatible because each requires a different type of compressor oil and desiccant. Since they are different, federal law prohibits mixing the two to prevent cross contamination. It is also federal law that shops doing A/C work are required to recover and recycle R-12 whenever they perform any repairs to an R-12 system.</p>
<p style="text-align: justify">Even though they are different, R-134a can be used in an R-12 system provided the system is converted or "retrofitted" to the new refrigerant. The way this is done will vary from one vehicle to another, but in most cases it will require:</p>
<ol>
    <li>Removing and recovering all the old R-12 refrigerant from the system.</li>
    <li>Changing the desiccant (accumulator or receiver/drier) to one that is compatible with R-134a.</li>
    <li>Adding compressor oil that is compatible with R-134a (PAG or POE oil)</li>
    <li>Installing R-134a fittings (which are different from the threaded fittings on R-12 systems.</li>
    <li>Recharging with system to about 80 percent capacity with R-134a refrigerant.</li>
    <li>Labeling the system to identify it has been converted to R-134a.</li>
</ol>
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<h3>The New Refrigerant - R134a:</h3>
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<h3>Accumulator:</h3>
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<h3>Receiver-Drier:</h3><br><br>
<h3>About the Author</h3>
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Keywords: <b>automotive air conditioning</b>

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