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Oil from compresser in line set

Went to a job today for no a/c and found a 5-ton condenser connected to a 3-ton air handler. Was going out on high head, so the 5-ton was pulled and got a 3-ton condenser...the real mystery came when the line set was cut it was full of oil ??? cleaned and flush and vac-ed installed the new condenser and every thing worked fine. My question is why was the while system full of oil when i cut the 5-ton out ?? everything is OK now...but how did the oil get out of the comp...any input appreciated....


  • Ironman
    Ironman Member Posts: 7,076

    The compressor crankcase is in the refrigerant circuit and some oil gets pumped out along with the gas (about 5%).  Again, this is normal

    Two key things are necessary to get the oil back to the compressor as it gets pumped through the system:

    1. You must have a proper charge of refrigerant. If it's low, the oil can become logged in the evaporator and the compressor will be deprived of lubrication. This is the most common cause of compressor failure.

    2. The piping must be done correctly according to manufacturer's spec's and good practice. This involves proper sizing, sloping, traps only where needed and spec'd, etc. You don't want to configure the piping in a manner that will trap oil and prevent it from returning to the compressor. I'm referring particularly to a horizontal run in the suction line between the evaporator and the compressor. Traps may be necessary if the compressor is substantially higher than the evaporator to aid in oil return. But that would be in a vertical line and manufacturer's guidelines should be followed. A simple rule is: don't trap it unless the manufacturer says to.

    Because it's normal for oil to be carried with the refrigerant, you will usually see an oily spot where there's a leak in the system.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Techman
    Techman Member Posts: 2,144
    edited June 2011

    How much oil did you get out of the system? A few other possibilities could be dirty air filters/evap coil/ squirlle cage blower.Running the unit when it's cold outdoors or a freon leak also.But ,if it as full as you say,where did the oil come from? Was the 5t the original cond unit for the system? What happened to the cond  unit before the 5t ? In a compressor  changeout situation, the ammount  of oil in the old compressor is supposed to be measured,so you know whats comming when you start up that new unsuspecting compressor .Plus , if,seeing that dirty filthy oil you also have a clean up job on your hands.
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