No risk of operation beyond the application envelope.
No DGT protection required.
High and low pressure protection
High pressure
A high-pressure (HP) safety switch is required to shut down the compressor should the discharge pressure exceed
the values shown in the table section “System pressure test”. 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.
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. Danfoss CH 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 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.
Table 10: Pressure settings
Pressure settings
R410A
Working pressure range high side bar (g)
16.2 - 41.6
Working pressure range low side bar (g)
2.15 - 10.7
Maximum high pressure safety switch setting bar (g)
46.1
Minimum low pressure safety switch setting
(1)
bar (g)
1.5
Minimum low pressure pump-down switch setting
(2)
bar (g)
2.15
(1)
LP safety switch shall never be bypassed and shall have no time delay.
(2)
Recommended pump-down switch settings: 1.5 bar below nominal evap. pressure with minimum of 2.15 bar(g)
(1)
LP safety switch shall never be bypassed and shall have no time delay.
(2)
Recommended pump-down switch settings: 1.5 bar below nominal evap. pressure with minimum of 2.15 bar(g)
NOTE:
Note that these two different low pressure switches also require different settings. The low pressure pump down
switch setting must always be within the operating envelope, for example 2.15 bar for R410A. The compressor can
be operated full time under such condition. The minimum low pressure safety switch setting may be outside the
normal operating envelope and should only be reached in exceptional (emergency) situations, for example 1.5 bar
for R410A.
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.
CC-0042
T
T
TH
TH
KA
A1
A2
A3
A1
180 s
A2
KA
~
~
Please contact Danfoss Technical Support for any deviation from these guidelines.
Scroll compressors, CH290 and CH485 | Application
© Danfoss | Climate Solutions | 2022.09
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