GENER
AL INFORMA
TION
PR
ODUC
T INFORMA
TION
SY
STEM DESIGN
INTEGR
ATION INT
O SY
STEM
ORDERING INFORMA
TION
Control logic
Safety control logic
requirements
Tripping conditions
Re-start conditions
Value
Time
Value
Time
HP switch
See Pressure settings table
from section “Manage
operating envelope”
Immediate, no delay.
No by- pass
Conditions back to normal.
Switch closed again
Manual reset
LP safety switch
Maximum 5 auto reset during
a period of 12 hours, then
manual reset.
High pressure
According to EN378-2, a high-pressure (HP) safety
switch is required to shut down the compressor.
The high-pressure switch can be set to lower
values 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. The HP
switch must be connected to the CDS303 input
37 or an external contactor placed before and
after the drive.
Low pressure
A low-pressure (LP) safety switch must be
used. Deep vacuum operations of a scroll
compressor can cause internal electrical arcing
and scroll instability. VZH compressors exhibit
high volumetric efficiency and may draw very
low vacuum levels, which could induce such
a problem. The minimum low-pressure safety
switch (loss-of-charge safety switch) setting is
given in the following table. For systems without
pump-down, the LP safety switch must either 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. LP switch settings
for pump-down cycles with automatic reset are
also listed in the table below. Lock-out circuit or
LP switch or series with other safety devices must
be connected to CDS303 input 27.
OEM need to set port 27 to “coast inverse or
external interlock” to get rid of minimum running
time restriction.
Electronic expansion valve
Reverse rotation protection
With variable capacity systems, an electronic
expansion valve (EXV) is the strongly
recommended solution to handle refrigerant
mass flow variations. Danfoss recommends the
use of ETS products. Ramp-up and ramp-down
settings, of both EXV and compressor, must be
done with great care.
Ramp-up of the EXV must be shorter than
the ramp-up of the compressor, to avoid any
low pressure operation on suction side of the
compressor. The EXV can also be opened, up
to a certain degree, before the start up of the
compressor.
Ramp-down of the EXV must be longer than the
ramp-down of the compressor, also to avoid low
pressure operation (except with pump-down).
EXV should be closed, and remain closed,
when the compressor is off, to avoid any liquid
refrigerant entering the compressor.
Due to drive protection, compressors could work
properly even if the power connection between
the drive and mains is dis-matched. However, the
wires between compressor and drive must be
connected accordingly. To protect compressors
from reverse rotation, pressure difference could
be checked as a reference value. Use pressure
sensors to monitor pressure difference between
discharge and suction of the compressor, and for
normal operation, discharge pressure should be
at least 1 bar higher than suction pressure within
30 s running after compressor starting.
SY
STEM DESIGN
38
AB237586440343en-000601