• For the initial charge, the compressor must not run.
• Charge refrigerant as close as possible to the nominal system charge.
• This initial charging operation must be done in liquid phase between the condenser outlet and the filter drier.
If needed, a complement of charge can be done before evaporator, in liquid phase while compressor is running by
slowly throttling liquid in.
Never bypass safety low pressure switch.
For more detailed information see “Recommended refrigerant system charging practice“
Dielectric strength and insulation resistance tests
Several tests have been performed on each compressor at the factory between each phase and ground.
• Dielectric strength test is done with a high potential voltage (hi-pot) of 2Un +1000 V AC at least, and leakage
current must be less than 5 mA.
• Insulation resistance is measured with a 500 V DC megohm tester and must be higher than 1 megohm.
Recommendations:
• Additional dielectric test is not recommended as it may reduce motor lifetime. Nevertheless, if such as test is
necessary, it must be performed at a lower voltage.
• Insulation resistance test can be done.
• The presence of refrigerant around the motor windings will result in lower resistance values to ground and higher
leakage current readings. Such readings do not indicate a faulty compressor. To prevent this, the system can be
first operated briefly to distribute refrigerant.
Do not use a megohm meter nor apply power to the compressor while it is under vacuum as this may cause
internal damage.
Commissioning
Preliminary check
Check electrical power supply:
• Phase order: Reverse rotation is obvious if the compressor do not build up pressure and sound level is abnormal
high
DSF compressors are equipped with an electronic module: reverse rotation will be automatically detected. For more
details refer to section
• Voltage and voltage unbalance within tolerance: For more details refer to section
.
Initial start-up
• Crankcase heaters must be energized at least 6 hours in advance to remove refrigerant.
• A quicker start-up is possible by “jogging” the compressor to evacuate refrigerant. Start the compressor for 1
second, then wait for 1 to 2 minutes. After 3 or 4 jogs the compressor can be started. This operation must be
repeated for each compressor individually.
System monitoring
The system must be monitored after initial startup for a minimum of 60 minutes to ensure proper operating
characteristics such as:
• Correct superheat and subcooling.
• Current draw of individual compressors within acceptable values (max operating current).
• No abnormal vibrations and noise.
• Correct oil level.
© Danfoss | Climate Solutions | 2023.06
AB309735209512en-000603 | 57
Scroll compressors, DSF090 to DSF530 | Application
