TM_s-MEXT_ME28relC_00_12_19_EN
Technical manual
TRANSLATION OF THE ORIGINAL INSTRUCTIONS
93
12
PRESSURE PROTECTION AND CONTROL FUNCTIONS
In Split Type units, the condensation pressure (HP) is controlled by the external condensing unit. However, there is the need to control and protect the unit from excessively
low evaporation pressures (LP), and keep them within certain operating limits.
For this, and to ensure the safety of the unit, several protection levels (functions) are available, outlined in the chart that follows.
LP
PROTECTION
LP
ALERT
LP
NORMAL
SAFETY
REDUCTION LOAD
LP
FROST-FREE
LP(bar)
EVAPORATION PRESSURE
Figure 12-1:
Chart showing the LP pressure safety functions
Protections against low pressures (LP)
:
•
Safety Reduction Load LP.
•
Frost-free function, which follows the low pressure probe
The following paragraphs explain the above functions.
12.1
FROST-FREE FUNCTION WITH LOW PRESSURE PROBE
This function enables to control and prevent the formation of frost on the evaporator coil.
If the low pressure value falls below a set point, and remains there for a time that can be set in the parameter, the compressor is deactivated and the corresponding alarm is
generated. In any case, this will respect the safety times (minimum ON time).
When the low pressure read by the probe goes back above a value equal to set + differential, the compressor will be enabled again. In any case, this will respect the safety
times (minimum OFF time and minimum ON-ON time).
INFORMATION
The handling of the
alarm starts with a delay equal to the “low pressure activation delay” parameter value from the turning on of the compressor
(default value 180s).
The reset of the alarm is Automatic for a number of interventions/hour defined by the parameter. Once this value is reached, the alarm reset will pass to Manual reset.
The count of the number of interventions per hour can be deactivated. If deactivated, the alarm can only be resent in Manual.
The diagram below illustrates the function described above.
Time
(min)
P20.47
ON
OFF
P20.48
P20.49
P20.49
Compressor
P20.49 = Frost-free function activation delay time
P14.04 = Low pressure alarm delay
Start time count
P20.49
ON
OFF
Alarm
Manual
Automatic
Reset
Enable compressor
functioning
P20.51
Number of interventions per
hour for the frost-free function
60 min
P14.04
Figure 12-2:
Graph of the frost-free function with control on low pressure
The parameters to enable and configure the frost-free function are under the
“Regulations” menu
, which can be accessed by entering the
“Service” password
.
For the default values, see the parameters table.
