A
PPLICATION
GUIDELINES
15
FRCC.PC.017.A1.02
O
PERATING
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
suffi
ciently 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 recommend-
ed to shut down the compressor should the dis-
charge 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 com-
pressors is almost directly proportional to dis-
charge 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 recommend-
ed. Deep vacuum operations of a scroll compres-
sor can cause internal electrical arcing and scroll
instability. Performer® Heat Pump scroll compres-
sors exhibit high volumetric effi
ciency and may
draw very low vacuum levels, which could in-
duce 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 op-
erations 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 guar-
antees a minimum compressor running time of 2
minutes so as to provide for suffi
cient motor cool-
ing 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 in-
cludes 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
Condensing temperature °C
Example 1
HP2
LP2
LP1
HP1
Example 2
d
c
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
LP safety switch shall never be bypassed.
Depends on the models, check on the nameplate
Discharge line
Insulation
Bracket
Thermostat