Figures 6, 7 and 8 show different oil levels when a
single compressor is running. The photos in each
figure show the right and left sight glass of the
same compressor. If the level is not the same in
each glass, consider the true oil level to be the
lower level. The difference in levels is due to the
rotation of the crankshaft. The crankshaft and
running gear are producing the windage required to
push the oil down on one side while raising it on the
other. Reversing the direction of rotation of the
motor will reverse this relationship.
To check for excessive system oil charges, it is
compressors in the system be brought down to
approximately 1/4 of the sight glass. If the system
is overcharged, the oil levels will rise to a 1/2 sight
glass level within a short time (usually within an
hour). Continue removing oil until the oil level does
not rise after removal.
It is also recommended that the oil levels be kept at
this 1/4 level, or between the levels shown in
Figure 8. This is especially true if any compressors
have experienced any repeat gasket failures. To
summarize the advantages of keeping the oil at this
1. It ensures that excessive oil is not being lodged
in the system. This will elt1nste many gasket
2. The compressor, oil and motor run cooler 200 or
more in many cases.
FIGURE 6 HIGH OIL LEVEL
The oil level in Figure 6 is at least 7/8 of a sight
glass. Note the high oil level in the left sight glass
and solid foam in the right sight glass. Anytime the
glass is filled with foam, excessive oil is indicated
and oil should be removed.
FIGURE 7 BETTER RUNNING OIL LEVEL
The oil level in Figure 7 is 3/8 1/2 of a sight glass.
This is an acceptable oil level on single compressor
systems but does not always. give a true indication
of an excessive oil charge on multiple compressor
FIGURE 8 PREFERRED RUNNING OIL LEVEL
The oil level in Figure 8 is 1/8-1/4 of a sight glass.
The sight glasses are showing a different level
because of the crankcase rotation. Note the
amount of clear glass above the levels. These
levels will ensure against the possibility of
excessive oil in the system.