Vacuum evacuation and moisture removal
Moisture obstructs the proper functioning of the compressor and the refrigeration system. Air and moisture reduce
service life and increase condensing pressure, and cause excessively high discharge temperatures, which can
destroy the lubricating properties of the oil. Air and moisture also increase the risk of acid formation, giving rise to
copper platting. All these phenomena can cause mechanical and electrical compressor failure.
For these reasons it’s important to perform a vacuum dehydration on the system to remove all residual moisture
from the pipe-work after assembly; CH compressors are delivered with < 100 ppm moisture level. The required
moisture level in the circuit after vacuum dehydration must be < 100 ppm for systems with a CH.
• Never use the compressor to evacuate the system.
• Connect a vacuum pump to both the LP & HP sides.
• Evacuate the system to a pressure of 500 μm Hg (0.67 mbar) absolute.
Do not use a megohm meter nor apply power to the compressor while it’s under vacuum as this may cause internal
damage.
Refrigerant charging
For the initial charge the compressor must not run and eventual service valves must be closed. Charge refrigerant as
close as possible to the nominal system charge before starting the compressor. This initial charging operation must
be done in liquid phase. The best location is on the liquid line between the condenser outlet and the filter drier.
Then during commissioning, when needed, a complement of charge can be done in liquid phase: slowly throttling
liquid in on the low pressure side as far away as possible from the compressor suction connection while compressor
is running. The refrigerant charge quantity must be suitable for both summer and winter operations. Vacuum or
charge from one side can seal the scrolls and result in a non-starting compressor. When servicing, always ensure
that LP/ HP pressures are balanced before starting the compressor.
Be sure to follow all government regulations regarding refrigerant reclamation and storage.
For more detailed information see “Recommended refrigerant system charging practice” news bulletin FRCC.EN.050.
Dielectric strength and insulation resistance tests
Insulation resistance must be higher than 1 megohm when measured with a 500 volt direct current megohm tester.
Each compressor motor is tested at the factory with a high potential voltage (hi-pot) that exceeds the UL
requirement both in potential and in duration. Leakage current is less than 0.5 mA.
CH scroll compressors are configured with the pump assembly at the top of the shell, and the motor below. As a
result, the motor can be partially immersed in refrigerant and oil. 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.
In testing insulation resistance, Danfoss recommends that the system be first operated briefly to distribute
refrigerant throughout the system. Following this brief operation, retest the compressor for insulation resistance or
current leakage.
Never reset a breaker or replace a fuse without first checking for a ground fault (a short circuit to ground). Be alert
for sounds of arcing inside the compressor.
Commissioning
The system must be monitored after initial startup for a minimum of 60 minutes to ensure proper operating
characteristics such as:
• Proper metering device operation and desired superheat readings
• Suction and discharge pressure are within acceptable levels
• Correct oil level indicating proper oil return
• Low foaming in sight glass and compressor sump temperature 10K above saturation temperature to show that
there is no refrigerant migration taking place
Scroll compressors, CH290 and CH485 | Application
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