Refrigeration compressors with too much oil? No, I'm not talking about the oil sight glass being higher than normal.
I talking about the compressor crankcase filling up with oil!! Large amounts of oil!!!
How is it possible to have too much refrigeration oil in the compressor?
It should be a simple procedure. Add oil until the sight glass on the compressor is 1/3 to 1/2 full.
No more, no less, right???
Ahhh, if only it were that simple!!!
In the real world of refrigeration the oil level is dependent upon many factors.
Does the compressor have a working crankcase heater? Without the heater refrigerant mixes with the oil. When the compressor starts, the oil flushes out of the crankcase.
Is the expansion valve superheat properly adjusted? Too low a superheat setting allows liquid refrigerant into the crankcase. It mixes with the oil and washes it into the system.
Is the evaporator clean? Dirty coils can also allow liquid to flood back to the compressor.
Is the evaporator moving the right amount of air? Dirty coils, damaged fan blades, wrong motor rotations, all can allow liquid refrigerant in the crankcase.
Is the refrigerant piping installed correctly? Is it sized correctly? Are traps installed on risers?
So much to look for!!!
Want a typical in the field scenario???
A new customer has a problem. When I arrived on the job, I was informed that the down cooler had a history of repeated failures.
The condensing unit constantly tripped the oil safety control. Shutting the cooler down.
Of course the first thing I noticed, no working crankcase heater.
After resetting the control, the oil in the sight glass began to foam violently and left the crankcase. In refrigeration compressors that's always a sign of refrigerant in the oil.
Slowly the oil level returned to the crankcase. The longer the compressor ran, the more oil returned.
I shut down the compressor and installed a new crankcase heater.
Success!!! On to the next job!!!
Returning the next day, I checked the sight glass. Whoa!!! The level was very high!!!
I immediately shut down the unit. Too much refrigerant oil can destroy a compressor. I removed the excess.
After restarting the compressor, to my amazement the level continued to rise!
Once again I removed the excess. Once more the level began to rise!!!
Over and over I repeated this process. Each time removing more and more refrigerant oil.
What was going on???
You guessed it!!! Each time the control was reset, the oil foamed and disappeared. So
someone added more!!!
The system was oil logged. By oil logged, I mean excess oil in all the refrigerant lines, condenser coil, and evaporator coil.
What's that??? How could too much oil in refrigeration compressors cause the oil pressure control to trip???
Remember that crankcase heater?
During off cycles the oil was becoming saturated with refrigerant. When the compressor started, the oil pump began pumping this mixture.
Pumps do not work properly with refrigerant present. Eventually the oil pressure control shut down the condensing unit.
Yep, you know what happened next!!! Along comes someone to reset the control and add more refrigerant oil!!!
Refrigeration compressors making their own oil??? When you sit and watch that level go up and up and up, it makes you scratch your head and wonder!!!
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