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 7: 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.
© Danfoss | Climate Solutions | 2022.09
AB236986442743en-000501 | 15
Scroll compressors, CH290 and CH485 | Operating enevlope data