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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.
3.5
System protection for operation below atmospheric pressure
WARNING
Operation below atmospheric pressure! Fire hazard! During operation
below atmospheric pressure, a flammable mixture can form inside the system.
Ensure system tightness to prevent any ingress of air.
YRH(V)*KTE
compressors used in R454C systems could be operated below atmospheric pressure.
In that case special requirements for safety and tightness apply.
compressors used in R290 systems may be operated below atmospheric pressure only
YRH(V)*KTG
when installed in hermetically sealed systems. For non-hermetic systems, the pressure must always
be above atmospheric pressure. The operating pressure must be limited as defined by the operation
envelope – refer to the technical documentation.
When systems using YRH(V)*KTE/KTG compressors 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).
▪ A discharge temperature control is mandatory to stop the compressor when the maximum
discharge temperature is exceeded – see section 3.7 "Discharge gas temperature
protection".
▪ Additional warning notices shall be affixed to any system equipped with shut-off valves. The
warnings must contain instructions to open the shut-off valves completely after each repair or
maintenance work. The compressors may only be energized when the safety measures (high-
and low-pressure cut-outs and discharge temperature cut-out) have been checked and verified
to be operational.
NOTE: All of the above points must be fulfilled. If only one of them is not complied with, the
compressors shall not be operated below atmospheric pressure.
3.6
Crankcase heater
For stationary applications with permanent available power supply, crankcase heaters are the most
effective solution to keep liquid refrigerant out of the compressor oil during off cycles. For such
systems Emerson recommends the installation of a crankcase heater.
In transport and mobile applications, crankcase heaters are not effective since typically there will be
no voltage present during extended off-cycle periods.
A check valve in the discharge line along with a liquid line solenoid valve (pumpdown) should be
used to limit off-cycle migration to the compressor. The low leak check valve must be qualified for
discharge line service. See also sections 5.12 "Refrigerant migration" and 5.13 "Pumpdown
cycle".
10
AGL_AC_ST_YRH_EN_Rev01
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