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© STULZ SpA . – all rights reserved EN/36B/08.2018
4.6. Control, monitoring and safety components
All unit components are factory adjusted and generally do not require further adjustment. If, for
special reasons, it becomes necessary to change the adjustment settings of the automatic devices
these changes must only be performed by specialists who are experts on the product and only after
informing the STULZ engineering division department.
STULZ conditioners come with a set of devices designed to ensure proper operation. Tripping by
any one of these automatic safety devices is a sign of a malfunction and it is absolutely necessary to
eliminate the cause.
DANGER
It is forbidden to electrically by-pass the safety devices. Doing so, in addition to being
dangerous, also immediately invalidates guarantee coverage for the product.
Isolate the system from electric mains before performing any repair or maintenance work.
Work on the units must only be done by qualified and authorized experts.
High pressure switch (HP)
This stops compressor operation whenever pressure inside the refrigerant circuit exceeds 29.5 bar.
When pressure returns below 24.5 bar, alarm signal from high pressure switch is disabled.
Low pressure switch (LP)
This stops compressor operation when the pressure inside the refrigeration circuit drops below 0.4
bar When pressure returns above 1.5 bar, alarm signal from low pressure switch is disabled.
Contactors
These control the motors by operating with auxiliary voltage. They comply with IEC947-4-1
standards.
Automatic circuit breakers
These protect against overcurrents and short circuits. They have adjustable thermo-magnetic
tripping devices.
Temperature probes
Three PTC temperature probes are connected to analogue inputs of C2020 electronic controller, in
order to measure following parameters:
• intake of internal air temperature;
• surface temperature of evaporator (for antifreeze purpose);
• intake of external air temperature.
Pressure transducer (DP)
A pressure transducer with signal 4÷20 mA measures the condensing pressure and is connected to
an analogue input of C2020. Value of condensing pressure is used by C2020 to adjust condenser
fan speed according to the variable outdoor conditions.
Mechanical safety thermostat of heating elements (if present)
This protects the heating elements by cutting off the power supply in case of excessive surface
temperature of the heating elements. The thermostat is adjusted to 90°C.
Dirty filter alarm device RFS
This gives a dirty filter signal, shown both on the display and on a voltage-free contact. It indicates
when it is necessary to clean or replace the air filter.
