Operating conditions
Example 1
(R407C)
LP switch setting: LP1= 1.1 bar (g) (-20°C)
HP switch setting: HP1= 24.3 bar (g) (60°C)
The LP and HP switches don't protect
sufficiently from operation outside the
envelope. A DGT protection is required
to avoid operation in the hatched area.
Example 2
(R407C)
LP switch setting: LP2 = 2.3 bar (g) (-9°C)
HP switch setting: HP2 = 18.8 bar (g) (50°C)
The LP and HP switches protect from
operation outside the envelope. No
DGT protection required.
A high-pressure (HP) safety switch is
recommended to shut down the compressor
should the discharge pressure exceed the values
shown in the table below. 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.
Note: because power consumption of scroll
compressors is almost directly proportional to
discharge pressure, the high-pressure control can
be used to indirectly limit the maximum current
draw. A high-pressure control used in this manner
however can never replace an external overload
protector.
High pressure
High and low pressure
protection
A low pressure (LP) safety switch is recommended.
Deep vacuum operations of a scroll compressor
can cause internal electrical arcing and scroll
instability. Danfoss Heat Pump scroll 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 above 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 above.
Low pressure
On/off cycling (cycle rate
limit)
Danfoss recommends a restart delay timer to limit
compressor cycling. The timer prevents reverse
compressor rotation, which may occur during
brief power interruptions.
The system must be designed in a way that
guarantees a minimum compressor running time
of 2 minutes so as to provide for sufficient motor
cooling after start-up along with proper oil return.
Note that the oil return may vary since it depends
upon system design.
There must be no more than 12 starts per hour, a
number higher than 12 reduces the service life of
the motor-compressor unit. A three-minute (180-
sec) time out is recommended.
The discharge gas thermostat accessory kit
includes all components required for installation,
as shown below. The thermostat must be
attached to the discharge line within 150 mm
from the compressor discharge port.
Continuous operation ranges - R407C dew
10
20
30
40
50
60
70
-30
-25
-20
-15
-10
-5
0
5
10
15
20
Evaporating temperature °C
C
o
n
d
en
si
n
g
temperature
°C
Example 1
HP2
LP2
LP1
HP1
Example 2
R407C
Working pressure range high side
bar (g)
7.8 - 27.4
Working pressure range low side
bar (g)
0.7 - 6.6
Maximum high pressure safety switch setting
bar (g)
30
Minimum low pressure safety switch setting
bar (g)
0.5
Maximum test pressure
bar (g)
30
LP safety switch shall never be bypassed.
Depends on the models, check on the nameplate
Discharge line
Insulation
Bracket
Thermostat
18
FRCC.PC.017.A2.02
Application Guidelines
