My compressor(s) are having Lubrication Problems what could be the cause?

Compressor Lubrication Problems - Two Stage Compressors
ThermaCom are applying lessons learnt concerning incorrect Injection Cooling System set up and the grave affects this has upon the safety of the compressor lubrication function upon two stage compressors. Compressor maintainers are often not party to the designers thinking when the lubrication requirements were considered, and this may hamper diagnosis of premature or repeat compressor failure. Often the precise reasoning for certain aspects of system design may not be fully understood, and certainly this is common amongst Service Engineers faced with repairs to older equipment, which, by the time service compressor replacement falls due, is considerably past not only warranty, but often the units will be past current manufacture. With single stage compression systems many engineers will apply base principles to ensure the reason for compressor failure are eliminated, and by and large system design idiosyncrasies are relatively limited and most variations are commonly found and hence expected. The relative rarity of Two Stage compression systems effectively means many experienced service engineers will not be aware of the finer differences to be taken into account. In particular Inter-stage Cooling function is often misunderstood, particularly as the inter-stage pressure is largely a function of the amount of cooling available. On many two stage machines this is achieved by injecting liquid refrigerant into the 1st stage discharge manifold, and precise control is provided by an expansion valve phial located about 8 inches from the manifold. Over-injection will cause overcooling and thus a drop in pressure, whereas the obvious less thought out conclusion is that over injection would increase inter-stage pressure as more gas means more pressure, but in this case such a conclusion would be incorrect. The obvious conclusion from failing to take account of this point will be a potentially disastrous over injection of liquid refrigerant just where it is needed least, because the liquid is being injected at the direct return point through the normal suction port, from here it will take the normal oil return route via the piston rings directly to the crankcase. Once here dilution is swift and bearing damage almost inevitable. Outwardly this will manifest as a low inter-stage pressure. Our experiences also show that over injection may also cause premature 2nd stage discharge reed failure due to thermal shock of cold liquid refrigerant hitting hot valves. The important point to remember is liquid injection is to provide de-superheating only. Accurate pressure and temperature measurements and correct use of refrigeration comparator rules are essential to maintain close setting of the injection cooling. Just as important however is remembering to refit the sense phial correctly to the inter-stage connection pipework when the replacement is installed.