28
C6.1.6/0117-1017/E
2.17 Compressor motor protection
The electronic controller protects the compressor motor against the following:
▪
over current
▪
phase loss
▪
incorrect phase rotation
▪
voltage imbalance
If the compressor motor current exceeds a predefined (non-adjustable) current limit, the electronic
controller shuts the unit down and generates an error signal. For this function two of the main phase
supply lines to the compressor (compressor via the contactor) are routed through the current
sensors.
2.18 System pressure protection
2.18.1 High-pressure safety switch
A high-pressure switch is registered by the electronic board. The sensing device is a non-adjustable,
high-pressure switch that will open in the event of an abnormally high discharge pressure (above 28
bar on ZXME & ZXLE units, 28.8 bar on ZXDE units).
▪
The unit will stop then and restart automatically after a 5-minute delay and after unit pressure
has decreased to 21 bar (24 bar for ZXDE units).
▪
After 7 successive HP cut-outs over 1 hour, the unit will lock out. In this case a manual reset will
be necessary.
2.18.2 High pressure: pressure relief valve
There is a connection port sideways on the top of the unit liquid receiver for a pressure relief valve.
It is a thread with a ¼"-NPT for units with serial number up to 16AZ07042M (with one fan) and
16AZ07092 (with two fans)
.
From this serial number onwards, the 3/8"-NPT connection is used. The
pressure relief valve is not factory-assembled.
2.18.3 Low-pressure safety switch
– Optional
In a way similar to the high-pressure sensor, the electronic controller registers the switching action
of the adjustable low-pressure switch, which will open in the event of an abnormally low suction
pressure:
▪
The unit will stop then restart automatically after a 3-minute delay and when the unit reaches
the cut-in pressure level.
The unit is always equipped with a suction pressure transmitter which also takes care for protection
against vacuum operation. The use of the optional low-pressure cut-out will provide the highest
protection level for the unit. In rare instances of controller breakdown the optional low-pressure switch
would allow to run the unit in emergency mode.
2.19 Other inputs of the XCM25D controller
2.19.1 Customer-supplied control (room thermostat)
The electronic controller is equipped with a digital input (
DI3
) open/close signal (such as the switching
action of a normal commercial thermostat) and relays a similar action as an output to the compressor
contactor in the case of a thermostat-controlled (parameter "
C05
") system (see wiring diagrams in
Appendices 2 and 3
). If the system is controlled by low-pressure cut-out for a multiple evaporator
system and/or pump-down system, the controller XCM25D accepts signals directly from an
adjustable low-pressure switch (optional).
2.19.2 Case temperature controller
An alternative method of system temperature control can be used. The electronic controller accepts
an input from a common commercial thermostat (
DI3
, digital input). For details see Chapter 2.9.4
"Additional features for customization".
2.19.3 Ambient temperature sensor
An ambient temperature sensor supplied by Emerson is connected to the electronic controller. This
temperature sensor has several functionalities like emergency mode control, lower fan speed
