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6
CONTROLLER LOGIC
This chapter describes the logic of the controller fitted in roof top units.
The unit you have purchased may not be provided with all the functions illustrated in this manual, because each
unit is configured differently and has different accessories fitted.
6.1 General
The main purpose of the controller installed in the unit is to preserve the temperature and humidity conditions
in the place which is served by the roof top unit within the operating limits of the unit, as specified in the
technical book.
Depending on the unit configuration, the controller fulfils its purpose using different devices fitted in both the
aeraulic and refrigerant circuits. The controller also continuously checks that the unit operating parameters are
within the specified safety limits so as to prevent breakage of the unit and hazardous situations for both people
and the environment.
All the illustrated functions refer to correctly installed units, as specified in the
documentation supplied by the Manufacturer.
The parameters provided in this manual are indicative: their actual value may change
in function of the unit configuration and the type of installation.
6.2 Unit switch-on
The unit is in OFF mode when it is supplied with electricity, but it is not enabled for operation.
In this condition the controller displays the values read by the analogue inputs and the status of the digital
inputs and outputs. All the outputs are not automatically enabled by the controller, except for alarm outputs, if
any, as described later on.
The unit is switched on in one of the following ways:
using the keyboard;
by time slots, where enabled;
by the control system, only in cases where a BMS control system is enabled.
All the OK signals must be enabled if the unit is to be switched on. If at least one of the OK signals above is
missing, the unit will fail to get started.
6.2.1 Keyboard-controlled switch-on
The keyboard can be used to either start or stop the unit on condition that the remote ON/OFF digital input is
closed (ref. to unit wiring diagram).
First, make sure that the digital ON/OFF input is closed. Its status is viewed on screen I8 in the “Inputs/Outputs”
menu. Go to the main screen, press the Prg button, select the “Unit ON/OFF” option in the menu and press
Enter to confirm. Screen "N0" appears on the display.
Press the "Enter" button to change the status of the unit: if the unit is off, it turns on, and vice versa.
If the time slots are enabled, the unit only gets started if the current time slot is one of those enabled for unit
switch-on.
If a control system is used to monitor the unit, the unit gets started after receiving an OK signal via a serial line.
6.2.2 Time-zone-controlled switch-on
The software is used to control unit switch-on and switch-off based on weekly and daily time slots.
Weekly time slots are designed to set the days in the week when the unit is either on or off. At midnight the
controller checks the status of the unit programmed for the next day and either starts or stops the unit based
on the required setting.
A daily time slot can be set for days in which the unit is expected to be operational. More specifically, the
system enables setting of the summer and winter operating setpoints both inside and outside a daily time slot
in addition to activation of the unit on/off out of the scheduled time. The time slots are enabled and programmed
in the “Clock” menu of the controller.