Hi Regulator
low diff oil pressure on a screw can be a number of things. You would have to establish what way you oil pressure is generated, there are four common configurations.
1/ Continuously running oil pump which is separate from the main compressor, with it's own drive motor.
2/ Pre-lubrication oil pump which is as above, but only runs for a few minutes at start-up to establish oil pressure.
3/ Inbuilt oil pump, driven off the main compress or drive.
4/ No oil pump; differance between inlet and outlet (suction and discharge) creates the driving force for the oil (ol pressure is differance, less pressure drop in the oil piping and the oil filter)
The most common is the latter. When you have established what you have, the problem will become clearer.
If and only if you have the latter lubrication system, look for the following:
Low head pressures and high suction pressures, this will cause low oil diff.
If as I suspect you have a low head, elevate the head pressure, ie. the condenser fan settings (or just switch they off on initial start up until say 40 deg C condensing is developed). This will initially create the oil pressure until the refrigeration load is applied to the condenser, after which the oil diff will be self maintaining.
Regulator you also talked off low suction supheat, this is also possibly a product of low head pressure, to be correct the electronic valves are opening up to establish themselves, initially, with low head they have to open up to a high opening %, the head pressure then starts to establing rather rapidly, with the capacity of the valves increasing rapidly too and the electronic system has lag which alllows refrigerant carryover.
Hope this helps. Regards. Andy
Linear Mode
