Understanding the number of things that can prevent an air conditioner from functioning properly strikes many homeowners as a daunting task. Yet the fact is that certain AC ailments are much more likely to beset you than others. If you would like to improve your awareness of common air conditioning issues, read on. This article will discuss the frequently encountered problem of a restricted capillary tube.

The Capillary Tube

Before delving into the problem of a restricted capillary tube, it may be helpful to review a little bit about the function of this important components. The capillary tube is the simplest form of so-called metering device. This category of air conditioner component is responsible for restricting the flow of refrigerant as it exits the condenser unit en route to the indoor evaporator coil.

This restriction performs two key functions. First, it helps to lower the temperature of the refrigerant, thus ensuring that it will be at the ideal temperature for absorbing heat inside of the evaporator coil. Second, by restricting the flow rate, it also lowers the pressure. This also ensures that the refrigerant will be able to more easily absorb heat.


In order to perform these two important tasks, a capillary tube must be necessarily be quite narrow. In fact, the inner diameter of a capillary tube may be as small as 0.02 inches. This tiny diameter puts the capillary tube at significant risk of developing blockages as the result of contaminants or particulate matter. Such particles may block the flow of refrigerant entirely, or they may simply restrict the flow. Unfortunately, the latter issue is much more difficult to diagnose.

Effects Of Restriction

A restricted capillary tube will prevent an adequate amount of refrigerant to flow to the evaporator coil, thus causing the coil to become starved. As a result, the system's suction pressure will go down, forcing the compressor to work much harder to supply the evaporator coil with refrigerant. As a result of this increased difficulty, the system will be forced to run for longer times, thus leading to more internal heat and wear and tear.

Diagnosis Problems

As noted above, it can be difficult for a technician to accurately diagnose a restricted capillary tube. That's because the symptoms of this issue are very similar to that of another common problem: a low refrigerant charge. This is generally caused by a leak somewhere in the system. Both problems will affect the suction pressure and the cooling power of the system. In order to accurately identify the problem, it is often necessary to drain the refrigerant from the system and carefully measure it to determine if refrigerant has been lost through a leak. If not, it is much more likely that a capillary tube restriction is the source of the poor performance.

Talk to a company like Air Cool AC Inc for more information about your AC system.