R-Pro › Field cases › Freezers & ultra-low temperature
Two-stage compressor discharge gas temperature too high (oil carbonisation, viscosity loss)
Likely causes
Insufficient inter-stage cooling → the high-stage suction gas enters highly superheated
Check: Measure the discharge line temperature. With mineral oil lubrication the maximum allowable discharge gas temperature is 130–140°C. Above that the oil carbonises and loses viscosity, so lubrication fails. Also read the intercooler inlet/outlet temperatures and the interstage pressure.
What to do: Restore inter-stage cooling first — check and correct liquid-injection nozzle blockage, fouled intercooler coil, and interstage pressure set point drift. A closed flash inter-stage cooler is designed so the liquid in the condensing-pressure coil is subcooled to about 10 K above the intermediate saturation temperature. If the oil is already dark and thin, change the oil and filter drier and run an acid test.
💡 Why two stages: as evaporating temperature drops the compression ratio grows, and squeezing it all in one machine makes the discharge gas so hot the oil burns. So it is split into a low (booster) and high stage with the gas cooled in between. On a two-stage compressor the oil sump sits at intermediate pressure — do not judge oil level and oil return with single-stage habits.
All 565 cases work offline in R-Pro, with error codes for 62 brands and P-T data for 108 refrigerants.
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