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Understanding Air Conditioner Superheat

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As many homeowners learn the hard way, the cost of operating an air conditioning system can vary greatly depending on how efficiently it runs. Of course, in order to evaluate this efficiency, technicians have to rely on a number of sophisticated measurements. Some of the most important information comes from the temperature of the refrigerant in your evaporator coil.
Specifically, HVAC professionals gain valuable insight into your system's performance by measuring superheat. Unfortunately, many homeowners fail to understand the meaning of this term. If you would like to increase your knowledge of air conditioner superheat, keep reading.

Boiling Point

Before delving into the specifics of superheat, you will benefit from learning about liquid boiling points. Boiling point refers to the temperature at which a liquid crosses over into its gaseous state. When most people think of boiling point, they think of water. Water has a relatively high boiling point of 212 degrees Fahrenheit.
Yet not all liquids boil at such a high temperature. Refrigerant, for instance, has a boiling point many times lower. For example, the R-22 refrigerant possesses a boiling point of 40 degrees Fahrenheit. As liquid refrigerant absorbs heat inside of your evaporator coil, it soon reaches its boiling point, changing into a gas in the process.


Many people hold another common misassumption about boiling points. They imagine that once a liquid has achieved its boiling point and turned into a gas, it can no longer absorb heat. Yet in the case of gaseous refrigerant, its temperature remains quite low - much lower than the temperature of the air in your home.
As the gaseous refrigerant continues to circulate inside the evaporator coil, it continues absorbing heat. To determine the overall efficiency of an air conditioning system, contractors routinely measure the temperature of the refrigerant as it flows out of the evaporator coil. The temperature of the refrigerant doesn't mean that much, but the superheat is.
Superheat simply denotes how much heat the refrigerant has absorbed above its boiling point. In other words, say the refrigerant leaving your evaporator unit has a temperature of 55 degrees. That would mean that the refrigerant has a superheat value of 15.
Measuring superheat allows contractors to glean key information about the amount of refrigerant entering your evaporator coil and the overall energy efficiency of your system.


To minimize energy waste and potential component damage, superheat must fall within a predetermined threshold. This threshold varies from system to system, as it must take into account a wide variety of factors, like the distance from the condensing unit to the evaporator unit, as well as the overall cooling power of the system.
When superheat falls too low, your system stands at risk of refrigerant flooding. Flooding involves refrigerant switching back to its liquid state while inside of the return lines leading to the compressor. Flooding places extreme amounts of internal stress on the compressor. It also leads the refrigerant mixing with the compressor oil.
Excessive superheat can be just as problematic. High superheat leads to starving, which involves the loss of lubrication inside of the compressor oil. This loss stems directly from the high refrigerant temperature, which causes the oil in compressor crankcase to overheat and break down.
Eventually, the compressor oil will lose much of its viscosity. As a result, the oil no longer provides the lubrication needed to keep your compressor running smoothly. Mechanical breakdowns and overheating may soon ensue.
Measuring superheat is one of the most basic - and the most important - of all air conditioner diagnostic tests. To learn more about how to keep your system running strong, please contact the pros at Mega Air Conditioning, Heating & Electrical.

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