© 2018 Emerson Climate Technologies, Inc.
29
AE4-1431 R1
pressure MDP, high compression ratio HCR, low
density flow LDF, high density flow HDF.
•
Also perform tests for different system operations,
e.g., part load, defrost, bypass etc. Make sure the
tests cover all possible different system conditions.
•
Another method to determine if liquid refrigerant is
returning to the compressor is to accurately
measure the temperature difference between the
compressor oil crankcase and the suction line.
During continuous operation we recommend that
this difference be a minimum of 50°F (27°C). This
“crankcase differential temperature” requirement
supersedes the minimum suction superheat
require
ment detailed in section “
”.
To
measure
oil
temperature
through
the
compressor shell, place a thermocouple on the
bottom center (not the side) of the compressor shell
and insulate from the ambient.
During rapid system changes, such as defrost or ice
harvest cycles, this temperature difference may
drop rapidly for a short period of time. When the
crankcase temperature difference falls below the
recommended 50°F (27°C), our recommendation is
the duration should not exceed a maximum
(continuous) time period of two minutes and should
not go lower than a 25°F (14°C) difference.
Figure 21 - Testing points for oil return
behavior investigation
