Emerson Copeland YHV029RG Application Manuallines page 26

Once a new system design is set and assembled, a f unctional test is required. The f unctional test
includes a qualification for the general system oil return and a ref rigerant floodback and oil dilution
test.
A sample compressor equipped with an external oil sight tube can be ordered from Emerson for lab
testing.
Records of the evaporating temperature and the bottom shell temperature shall be taken with a high
sampling rate during the entire oil return or oil balance testing and under all tested conditions. The
liquid level in the sight tube has to be observed and recorded too. Testing conditions shall include
the different operation modes and varying loads. If the system is reversible, the tests should be
conducted in cooling, heating and defrost modes.
System engineers should review the system design and operation to identify the critical conditions
and to check oil return, oil balancing, liquid f loodback and oil dilution. Typically, the f ollowing
situations should be considered:
In single compressor systems: to check oil return, testing conditions shall be at minimum mass
f low and minimum density of suction gas in continuous and frequent start/stop-cycling.
In all systems: to test liquid floodback and oil dilution, all possible transient operation conditions
in the system should be checked, eg, compressor frequent start/stop, compressor start after long
of f time with migration, defrost, switching between the operation modes in reversible systems,
load changes, f ans or pumps cycling at low load and more. To evaluate the risk of liquid floodback
and oil dilution, please ref er to the charts in
compressor inlet have to be checked as well.
The bottom shell temperature together with the evaporating temperature gives an indication whether
liquid ref rigerant is returning or diluted in the compressor oil sump. The compressor sump
temperature must remain in the saf e area, which is above the continuous line, as shown in the oil
dilution charts in Figures 19 & 20. In case of operation in the unsafe area, which is under the dashed
line, adjustments are required in order to modify the system design, refrigerant charge or superheat
setting of the expansion device(s). The bottom shell temperature should be measured accurately.
The thermo-probe must be properly insulated and positioned on the opposite side of the sight glass
or at an angle of 90° to 180° clockwise from the suction inlet with view on the top.
Figure 18: Oil dilution chart for R290 and PAG (tb = bottom shell temperature; te = evaporating temperature)
AGL_HP_VS_YHV_RG_RT_EN_Rev00
Figures 18 & 19. Liquid level and superheat at
21