Carrier 17/19EX - Manual (Page 47)

During the machine start-up, the PIC will energize the oil pump and provide 15 seconds of
prelubrication to the bearings after the oil pressure is verified and before the controls start the
compressor. During shutdown, the oil pump will run for 60 seconds after the compressor
actually shuts down for the purpose of post-lubrication. The oil pump can also be energized for
testing purposes in controls test.
Ramp loading can slow the rate of guide vane opening to minimize oil foaming at start-up. If
the guide vanes open quickly, the sudden drop in suction pressure can cause any refrigerant in
the oil to flash. The resulting oil foam cannot be pumped efficiently; oil pressure falls off, and
lubrication is poor. If oil pressure falls below 15 psi (90 kPa) differential, the PIC will shut down
the compressor.
Oil reclaim is accomplished by returning the system oil through the check valve/orifice (Item
11). As oil builds up behind the second stage impeller, it is drained by the check valve/orifice
back into the oil reservoir. An oil/refrigerant mixture is drawn up from the operating level of the
cooler into the guide vane housing. This assists the oil return system at low load operating
conditions.
Click here for Figure 5 — Hermetic Compressor Lubrication System
(EX Compressor Shown)