High And Low Pressure Protection; Crankcase Heating; Oil Return Management - Danfoss VRJ Application Manuallines

Application Guidelines
High and low pressure
protection
Pressure settings
High pressure
Low pressure
High pressure ratio

Crankcase heating

Oil return management

Operating conditions
Suction and discharge pressure transmitters have
to be installed and connected to the variable
speed drive to ensure the compressor operates
within the application envelope described above.
Working pressure range high side
Working pressure range low side
Maximum high pressure safety switch setting
Minimum low pressure safety switch setting 
: LP safety switch shall never be bypassed
According to UL requirements, a high pressure
safety switch is still mandatory in any system,
even with high pressure transmitters connected
and used via the variable speed drive.
HP switch settings shall not exceed the maximum
service pressure of any system components. The
high-pressure switch can be set to lower values
A low pressure (LP) safety switch is
recommended. Deep vacuum operations of a
scroll compressor can cause internal electrical
arcing and scroll instability. Danfoss scroll
compressors exhibit high volumetric e ciency
and may draw very low vacuum levels, which
could induce such a problem. The minimum
Scroll compressors are machines with xed
volume ratio, and operate more e ciently
near the design pressure ratio. In the extreme,
do not exceed a 7.5:1 pressure ratio (absolute
discharge pressure to absolute suction pressure)
A crankcase heating function can be provided
by injecting a DC current in the motor of the
compressor, to keep the compressor warm, and
avoid liquid migration during o cycle.
A speci c function can be enabled to secure
the oil return to the compressor. When the
compressor is running at minimum speed for
Refer to "Danfoss VRJ Installation and Operation
instructions" for connection details, and to
"Sensor Selection Guideline" manual for selection
details and technical brochures about pressure
transmitters.
psig 119 - 645
psig 28 - 202
psig
psig
depending on the application and ambient
conditions. The HP switch must either be placed
in a lockout circuit or consist of a manual reset
device to prevent cycling around the high-
pressure limit. If a discharge valve is used, the HP
switch must be connected to the service valve
gauge port, which must not be isolated.
low-pressure safety switch (loss of charge safety
switch) setting is given in the above table. Either
the LP safety switch must be a manual lockout
device or an automatic switch wired into an
electrical lockout circuit. The LP switch tolerance
must not allow for vacuum operations of the
compressor.
for extended periods. The Danfoss VRJ scroll
compressor is equipped with an internal pressure
relief valve for protection against blocked
condenser and fan failure conditions.
Refer to "Danfoss VRJ Installation and Operation
instructions" for details.
extended periods, every half hour, speed will be
increased to 2400 rpm for a 80 seconds period.
AB141686422149en-US0401
R410A
653
22
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