Application guidelines
63
FRCC.PC.023.A7.22
Single compressors
This minimum run time is set to guaranty long
enough running time at start up in order to
create enough refrigerant flow velocity in the
system to recover the oil to the compressor
sump.
• Current draw of compressor within acceptable
values (RLA ratings)
• No abnormal vibrations and noise.
Installation
In installations with good oil return and line
runs up to 20 m, no additional oil is required. If
installation lines exceed 20 m, additional oil may
be needed. 4% of the total system refrigerant
charge (in kg) can be used to roughly define the
required oil top-up quantity (in liters) but in any
case the oil charge has to be adjusted based on
the oil level in the compressor sight glass. This
procedure must be conducted with the system
running at high load (compressor at full speed)
When the compressor is running under stabilized
conditions the oil level must be visible in the
sight glass.
The presence of foam filling in the sight glass
indicates large concentration of refrigerant in the
oil and / or presence of liquid returning to the
compressor.
Mandatory check is made at low load and
stabilised conditions, compressor at minimum
speed, for a minimum duration of 1 hour. The oil
level must be always visible at the compressor
sight glass. If any deviation is observed, this
means that some oil is trapped in the system,
heat exchangers and/or pipes.
The CDS303 frequency converter integrates an
oil recovery management algorithm which needs
to be adjusted in regards to the system design.
Oil return management function forces the
compressor to rotate at 4200rpm (70 Hz) for an
adjustable given period of time in order to build
a good refrigerant gas velocity in the system to
allow the oil recovery to the compressor sump.
This oil management function is factory preset
with the following parameters:
• 28-10 Oil return management : enabled
• 28-11 Low speed running time : 60 minutes. This
is the duration during which the compressor
rotation speed is below 3000rpm (50 Hz)
• 28-12 Fixed boost interval : 24 hours
• 28-13 Boost duration : 30 seconds
If the oil level decreases down to the bottom
side of the sight glass, parameter 28-11 must
be adjusted to start the boost cycle. During this
boost cycle the oil level in the sight has to be
monitored in order to adjust the boost duration
on parameter 28-13 to a value that allows the oil
level to be recovered at ½ of the sight glass.
The oil level can also be checked a few minutes
after the compressor stops, the level must be
between ¼ and ¾ of 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 idle. Use
the schrader connector or any other accessible
connector on the compressor suction line and
a suitable pump. See News bulletin “Lubricants
filling in instructions for Danfoss Commercial
Compressors”.
Oil level checking and
top-up
Note this compressor is equipped with
a four poles electrical motor so the applied
frequency from the inverter will be 50 Hz for
25 rps (1500 rpm) up to 200 Hz for 100 rps
(6000 rpm).
