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Air Conditioning Components Explained: The Capillary Tube

In order to provide your home with the desired amount of cooling, an air conditioner requires that all of its many components remain working within strictly specified limits. Unfortunately, many people fail to realize when such components fail to meet the minimum standards. Often this is because they do not understand the various components at play. This article will act to increase your knowledge of air conditioning mechanics by explaining the purpose of the component known as the capillary tube.

The Basics

The capillary tube consists of a coiled length of copper piping. This piping has a very narrow internal diameter--a fact that is critical to its overall effectiveness and purpose. The capillary tube can generally be found located inside of the condensing unit located outside of your home. The capillary tubes job is to alter the dynamics of the refrigerant as it moves between the condensing unit and the indoor evaporator.

Refrigerant Cycle

To understand the function of the capillary tube, it will first help to refresh your knowledge of the refrigerant cycle taking place inside of your air conditioner. This cycle begins with the compressor, which is responsible for increasing the pressure of the hot gaseous refrigerant being channeled out of the evaporator in your home. The refrigerant then passes through the condenser, which acts to change it into liquid form.

At this point, however, the temperature of the refrigerant is still fairly high. If it were to simply flow back into the evaporator at this point, it would not be able to achieve its cooling task very efficiently. Instead it passes through the capillary tube, which acts to reduce not only the temperature but also the pressure of the refrigerant, thus priming it to achieve the maximum amount of cooling.

Capillary Tube

The capillary tube is able to achieve these changes in the state of the refrigerant thanks to its constricted size, which immediately acts to lower the pressure of the refrigerant. The capillary tube is not the only manner of component capable of effecting this change. Rather it belongs to a class of components known as throttling devices. The capillary tube represents the simplest version of throttling device.

A capillary tube falls into the sub-category of non-adjustable throttling devices. This simple means that the flow of refrigerant through the capillary tube cannot be changed. On the contrary, it's flow rate is at the whim of such factors as the atmospheric pressure, refrigeration load, and other environmental factors. For most residential purposes, this limitation is perfectly fine. However, for more intensive and responsive air conditioning systems, the throttling device known as the thermostat expansion valve is used instead.

If you suspect that there is a problem with your capillary tube, contact an air conditioning repair specialist. 


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