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2 Common Causes of Expansion Valve Restriction

Air Compressor Mounted On Wall
One of the most important parts of your air conditioning system goes by the name of the expansion valve. The expansion valve acts to decrease the pressure of the refrigerant as it flows into the evaporator coil. This pressure change, in turn, causes the refrigerant to turn into a vapor, while also lowering its temperature.
The expansion valve plays a key role in preparing the refrigerant to absorb heat from your home's air. If the expansion valve becomes restricted — thus lowering the flow rate of refrigerant too greatly — serious problems can ensue. Unfortunately, restrictions occur all too commonly, thanks to the expansion valve's tiny orifice.
If you would like to learn more about your expansion valve and the problems it might experience, keep reading. This article outlines two common sources of expansion valve restriction.

1. Wax Buildup Inside the Valve

Most air conditioning compressors contain oil used to keep all of their moving parts correctly lubricated. This oil comes into direct contact with the refrigerant as it passes through the compressor. The speed of the refrigerant flowing through naturally carries a small amount of oil along with it.
Virtually all mineral-based oils contain a certain amount of naturally occurring paraffin wax. Even oils marketed as being wax-free usually still contain trace amounts of wax. Under normal conditions, this wax remains in solution. In other words, the wax remains a homogenous part of the oil itself.
Yet as conditions change, the solubility of the wax may be affected. Temperature plays a huge factor here. At high enough temperatures, any amount of wax could remain suspended in oil. As temperatures decrease, the carrying capacity of the oil will also decrease. If the wax content is high enough, this can lead to a separation of oil and wax.
As noted above, the expansion valve causes the pressure — and hence the temperature — of the refrigerant to drop. If the oil used to lubricate your compressor contains an excessive amount of wax, this wax may separate and solidify inside of the expansion valve. There the wax restricts the flow of refrigerant and can even block the refrigerant entirely.
Such wax buildups indicate that the oil used in your compressor is not fully compatible with your refrigerant. Until the oil has been drained and replaced with an appropriate variety, wax deposits will continue to accrue inside of your expansion valve.

2. Moisture Contamination

Under normal circumstances, the refrigerant in your system should never come into contact with water or moisture. Yet moisture can enter a system that has fallen into disrepair. Leaks, damaged system components, and improper refrigerant handling can all allow water into your refrigerant lines.
Unfortunately, such moisture can quickly lead to serious issues for your system, especially when allowed to mix with your compressor oil. The combination of oil and water often leads to the formation of sticky sludge. As this sludge makes its way through your system, the sludge often builds up inside of the expansion valve.
These sludge deposits can quickly cause problematic restrictions to the refrigerant flow. Furthermore, such sludge tends to have a highly acidic nature. If allowed to remain in place, the sludge will soon begin to corrode any and all metal surfaces it comes into contact. This corrosion eventually compromises the structural integrity of your system.
As corrosion proceeds, it also leads to the buildup of additional contaminants in the refrigerant lines. These contaminants result in further restrictions, often preventing refrigerant from moving through the expansion valve altogether.
Fortunately, most air conditioning systems contain a crucial component known as the filter drier. The filter drier effectively sequesters any moisture that gets into the system, preventing it from causing problems. Of course, if your filter drier has reached its maximum capacity, moisture may once more be free to wreak havoc.
For more information about how to prevent unwanted expansion valve restrictions, please contact the HVAC professionals at After Hours Heating & Cooling, LLC.