4. THERMOSTAT CONTROL
4.1 Thermostat control is based on comparing the temperature T1, the set point *SP and the hysteresis *HYS.
Example: SP= 2.0; HYS= 1.5, compressor Off with T1= +2.0° and On with T1= +3.5° (2+1.5).
The compressor only switches On again if the Off time period determined by CRT since the previous switchover has elapsed. Whenever
a very small hysteresis HYS must be maintained, it is advised that a suitable value for CRT is selected in order to reduce the number of
starts per hour.
4.2 If sensor T1 fails, the output is controlled by parameter CDC as a proportion of a 10 minute operating cycle.
Example: CDC=06, 6 minutes On, 4 minutes Off.
4.3 If door switch input control has been enabled (DS=YES), parameter CSD determines the delay between when the door is opened
and the compressor stopping.
* Actual setpoint and hysteresis depend on the selection I/II: in mode I, the reference parameters are SP and HYS while in mode II,
IISP and IIHY.
5. DEFROSTING
5.1 Defrosting starts automatically when necessary time has elapsed to obtain the defrosting frequency set with *DFR. For example,
with DFR=4 there will be 4 defrostings per 24 hours, so defrosting occurs once every 6 hours.
The internal timer is set to zero when power is applied to the controller and at each subsequent defrost start. When the controller is put
on a standby, the accumulated time count is “frozen” (is not incremented).
Defrosting may also be induced manually by keeping the button pressed for 2 seconds.
During a High Pressure alarm (see par. 7.3), defrost is suspended.
5.2 Once defrost has started, the outputs are controlled according to parameter DTY as per the following table:
TABLE 3
5.3 Defrost lasts for the time DTO but, if the evaporator probe has been enabled (T2=YES) and temperature DLI is achieved before
this time elapses, defrost will be terminated in advance.
If parameter DRN is greater than 0, before cooling starts all outputs will remain off for the time assigned to DRN. This phase, called
drain down, will allow a complete ice melting and the drain of the resulting water.
* The actual defrost frequency depends on the selection I/II: in mode I, the reference parameter is DFR while in mode II it’s IIDF.
6. EVAPORATOR FANS
6.1 During thermostatic control, the evaporator fans are controlled by parameter *FTC and FPC. With FTC=NO, the fans operate
continuously regardless of the FPC value set. Alternatively, when FTC=YES the evaporator fans will operate in conjunction with the
compressor (i.e. when the compressor runs the fans will run), but dependant upon the FPC value set they will On/Off cycle after the
compressor has stopped. With FPC set between 1 to 3, you will obtain On/Off ratios of respectively, 33%, 50% and 60% with fixed
60 second off times. Therefore, once the compressor has stopped, with FPC=1 (33%) the fans will run for 30 seconds and stay off for
60 seconds. If FPC=2 (50%) the fans will run for 60 seconds and remain off for 60 seconds; with FPC=3 (60%) the fans will run for 90
seconds and stay switched off for 60 seconds. This cycle pattern will continue until the compressor starts again. With FPC=0, the fans
will follow the compressor cycle only.
This fan control function aims at recovering the maximum cooling effect available at the evaporator as well as greatly reducing unwanted
heat generated by the evaporator fan motors, so increasing the energy efficiency. Cycling the fans also avoids air stratification, and
allowing the temperature measured by probe “T1” to be updated, and thus accurate. If the temperature to be maintained is above
freezing then the maximum humidity is maintained in the chilled environment.
6.2 If the LCD15 is connected to a door switch and door switch control is enabled (DS=YES), during thermostatic control if the door is
opened, the fans will be stopped immediately.
6.3 During defrost, the fans are controlled by parameter FID; with FID=YES the fans remain on all through defrosting. With FID=NO,
the fans will be stopped and will only re-start when the conditions in paragraph 6.4 have been met.
6.4 After defrosting, if probe T2 is active (T2=YES), temperature FDD provides evaporator fan re-start. So the evaporator fans will not
run until the evaporator has a temperature lower than FDD. If such condition doesn’t occur within 4 minutes following defrost termination,
the fans will however be switched on again.
INSTRUCTIONS FOR INSTALLATION AND USE.
DTY D
EFROST COMPRESSOR
OFF Off Off
ELE On Off
GAS On On
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