Refrigerant charge limit
Danfoss CH compressors can tolerate liquid refrigerant up to a certain extend without major problems. However,
excessive liquid refrigerant in the compressor is always unfavorable for service life. Besides, the installation cooling
capacity may be reduced because of the evaporation taking place in the compressor and/or the suction line instead
of the evaporator. System design must be such that the amount of liquid refrigerant in the compressor is limited. In
this respect, follow the guidelines given in the section: “Essential piping design recommendations” in priority.
Use the tables below to quickly evaluate the required compressor protection in relation with the system charge and
the application.
Table 11:
Model
Refrigerant charge limit (kg)
CH290
13.5
CH485
17
charge limit
Table 12: charge limit
BELOW charge limit
ABOVE charge limit
Cooling only systems, Packaged
units
No test or additional safeties required
Refrigerant migration and flood back test
Sump heater
Cooling only systems with re-
mote condenser and split sys-
tem units
Refrigerant migration and flood back test
Sump heater
Refrigerant migration and flood back test
Sump heater
Liquid receiver (in association with LLSV and pump
down)
Reversible heat pump system
Specific tests for repetitive flood back
Sump heater
Defrost test (For more details, refer to section ”Reversible heat pump system“)
Recommended
Required
No test or additional safeties required
NOTE:
For special conditions such as low ambient temperature, low refrigerant load or brazed plate heat exchangers
please refer to corresponding sections.
Please contact Danfoss Technical Support for any deviation from these guidelines.
Liquid flood back
During normal operation, refrigerant enters the compressor as a superheated vapour. Liquid flood back occurs
when a part of the refrigerant entering the compressor is still in liquid state. Danfoss CH scroll compressors can
tolerate occasional liquid flood back. However system design must be such that repeated and excessive flood back
is not possible.
A continuous liquid flood back will cause oil dilution and, in extreme situations lead to lack of lubrication and high
rate of oil leaving the compressor.
Liquid flood back test
Repetitive liquid flood back testing must be carried out under expansion valve threshold operating conditions: a
high pressure ratio and minimum evaporator load, along with the measurement of suction superheat, oil sump
temperature and discharge gas temperature.
During operations, liquid flood back may be detected by measuring either the oil sump temperature or the
discharge gas temperature. If at any time during operations, the oil sump temperature drops to within 10K or less
above the saturated suction temperature, or should the discharge gas temperature be less than 35K above the
saturated discharge temperature, this indicates liquid flood back.
© Danfoss | Climate Solutions | 2022.09
AB236986442743en-000501 | 33
Scroll compressors, CH290 and CH485 | Application
