AGL_HP_VS_YHV_RG_RT_EN_Rev00 15
3.4 Pressure safety controls
3.4.1 High-pressure protection
Applicable regulations and standards, for example EN 378-2, shall be followed to apply appropriate
control and ensure that the pressure never exceeds the maximum limit.
High-pressure protection is required to stop the compressor operating outside the allowable pressure
limits. The high-pressure control must be installed correctly, meaning that no service valve is allowed
between the compressor and the pressure protection.
The high-pressure cut-out setting shall be determined according to the applicable standard, the type
of system, the refrigerant and the maximum allowable pressure PS.
The high-pressure limiter has to be connected to the ED3/EV3 drive
see wiring diagrams in section
4.2 "Electrical installation".Normally the high-pressure limiter must be closed. If the limiter is open,
the drive will not operate.
NOTE: For detailed specifications and instructions on how to connect the high-pressure
limiter to the drive, please refer to the ED3 & EV3 User Manuals.
3.4.2 Low pressure protection
CAUTION
Operation outside the application envelope! Compressor breakdown!
low-pressure protection should
be fitted in the suction line in order to stop the
compressor when it operates outside the envelope limits. Do not bridge or by-
pass the low-pressure limiter.
Applicable regulations and standards shall be followed to apply appropriate control and ensure that
the pressure is always above the required minimum limit.
Low-pressure protection is required to stop the compressor operating outside the allowable envelope
limits. The low-pressure control must be installed correctly into the suction line, which means that no
service valve is allowed between the compressor and the pressure protection.
The minimum cut-out setting shall be determined according to the refrigerant and the allowed
operation envelope
see Select software at www.climate.emerson.com/en-gb/tools-resources.
3.5 System protection for operation below atmospheric pressure
Operation below atmospheric pressure! Fire hazard!
below atmospheric pressure, a flammable mixture can form inside the system.
Ensure system tightness to prevent any ingress of air.
YHV*RT compressors in R454C systems can be operated below atmospheric pressure. In that case,
special requirements for safety and tightness have to be applied.
YHV*RG compressors in R290 systems may be operated below atmospheric pressure only when
installed in hermetically sealed systems. For non-hermetically sealed systems, the pressure must
always be above atmospheric pressure. The operating pressure must be limited as defined by the
operation envelope ref er to the technical documentation.
When YHV*RG/RT compressor systems operate below atmospheric pressure, the following
precautions must be observed.
Check all the critical points on the system and piping connections; tightness has to be ensured
also at very low pressure.
Minimum absolute working pressure: 0.5 bar.
The installation of mechanical high-pressure and low-pressure cut-outs is mandatory. For
systems provided with a service shut-off valve on the discharge side of the compressor, only a
mechanical pressure cut-out shall be used. Electronic pressure limiters, which could cause
delayed sensor response, are not allowed.
The high- and low-pressure cut-outs must be installed correctly on the discharge and suction
lines, which means that no service valve is allowed between the compressor and the pressure
protection (refer to EN 378 or ISO 5149).
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