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7.4.
Oil Level
When the compressor is running under stable conditions the oil level must be visible in the sight
glass. The presence of foam filling the sight glass indicates large concentration of refrigerant in
the oil and/or presence of liquid returning to the compressor. The oil level can also be checked
a few minutes after the compressor is shut down, the level must be between ¼ and ¾ of the
sight glass. When the compressor is OFF, the level in the sight glass can be influenced by the
presence of refrigerant in the oil.
Always use original Danfoss POE oil 160SZ from new cans. Top-up the oil while the compressor
is at idle. Use a Schrader connector or any other accessible connector on the compressor
suction line and a suitable pump.
7.5.
Variable Frequency Drive
There are tremendous energy saving and application advantages available by applying a
Variable Frequency Drive (VFD) drive to compressor cooling. Variable speed control offers the
ability to match the cooling capacity to the actual need. Costs are reduced through direct energy
savings of operating at a lower speed. The drive can operate a variable capacity compressor
over a wider range. Other advantages of the VFD are limiting the number starts and reduced
start system shock thus reducing peak energy demand and system wear. Below is a figure
showing the VFD control display and some general instructions required to charge the unit and
monitor any alarms.
The local control panel (LCP) for the VFD drive is the combined display and keypad on the front
of the unit. The LCP has several user functions:
•
Start, stop, and control speed when in local control mode
•
Display operational data, status, warnings and cautions
•
Programming frequency converter functions
•
Manually reset the frequency converter after a fault when auto-reset is inactive