Frost-Free Function With Low Pressure Probe - Mitsubishi Electric Evolution+ s-MEXT Technical Manual

As indicated by the chart, the alert level is bypassed if the fan is already running at 90% of the maximum nominal speed.
The way the function works can be displayed from the "Unit" menu.
13.1.2

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 sent by the parameter, the compressor
is deactivated and the corresponding alarm is generated. In any case, this respects 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 180 s).
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.
Start time count
P20.48
P20.47
ON
Compressor
OFF
ON
Alarm
OFF
Manual
Reset
Automatic
Version 38
Enable compressor functioning
P14.04 P20.49
Figure 12-7: graph of the frost-free function with control on low pressure.
P20.49= Frost-free function activation delay time
P14.04= Low pressure alarm delay
P20.49
P20.51
Number of interventions per hour for the
frost-free function
P20.49
Time (min)
60 min
173