Certain chemicals, welding residues, etc.., can, in the presence of air, trigger chemical reactions and destroy oil molecules. This situation, if associated with a high delivery temperature and with the temperatures caused by friction, it can give rise to the formation of acids, mud, or combination of both.

Causes of Contamination by Air and Foreign Bodies

Contamination caused by air and foreign bodies is generally due to installation errors. Foreign bodies can be prevented from entering the circuit ensuring that, when installing the system, only clean pipes are used. During the welding of the junction elements, contamination with the ambient air can be avoided by circulating dry nitrogen. The refrigerant circuit may also be contaminated during normal operation when adding the oil in the compressor. In fact the oil oxidizes very easily and can therefore drag air and humidity with it when topping up. The oil should be kept in storage with a layer of inert gas in surface.

Oxides

The oxides can appear in the form of:

• Red copper oxide
• Black copper oxide
• Red iron oxide
• Black iron oxide

The exact nature of the oxides cannot be determined on the site, based on a simple visual analysis: to know precisely the type of oxide present in the circuit it is necessary to make a chemical analysis. Furthermore, the combination of different contaminants that can be found in a refrigeration circuit produces blackish deposits that are difficult to identify.

Naturally, a contaminated filter reduces the lubrication of the compressor bearings connecting rod heads, and causes scratches or grooves on the moving parts, as happens in the case of a lowering of the oil level or in the case of overheating of the oil. Moreover, in case of presence of oxides, fragments of oxidized materials can often be seen encrusted on the less hard surfaces of the bearings. The extent of the damage depends on the reduction of the lubricant flow rate; the bearings located further away from the pump, in the lubrication circuit, are the first to be interested. Since the cylinder walls are lubricated in a splash, the piston bells should not show any particular wear.

Causes of Oxides Presence

The formation of oxides on the inner walls of the pipes is caused by heating in the presence of air during silver solder of the joints. If oxides are found in the oil, they can be removed from the circuit by installing a filter, or a filter drier, in the line of suction to retain oxides before they can penetrate into the compressor. The oil must then be changed as necessary, until it remains clean.