ALFA(NET) 75 RTDF -50/+50°C Doc.no.: 150014
version 1.0
Page 3of 8
9Defrost control
The automatic defrost is started by the defrost cycle-time (P30) and stopped by the maximum
defrost-time (P31) or sooner by reaching the maximum defrost-temperature (P32). Further has
the ALFA(NET) 75 RTDF additional parameters to control defrost;
Parameter 24: Defrost mode
The ALFA(NET) 75 RTDF has two defrost modes;
P24 = 0 While defrosting only the fan activates. (Natural defrost)
P24 = 1 While defrosting the relay DEFR. Activates. (Hotgas / Electrical defrost)
Parameter 34: Defrosting on compressor-time (if P60 = 0)
P34 = 0 In this case parameter 30 is the chosen defrost interval-time.
P34 = 1 In this case the defrost is started as the compressor has been active for
“parameter 30”hours.
Parameter 60 = 1: Defrost based on real-time clock
In this case the defrost is started at fixed times, set with parameters P61 until P72.
Parameter 36 = 1: The ALFA(NET) 75 RTDF starts with defrost on power-up
After power-up the ALFA(NET) 75 RTDF first starts with a delay of “parameter 37” minutes
before starting defrost, while in delay the ALFA(NET) 75 RTDF works normally.
Parameter 33 = 1: Compressor active at defrost. (if P24 = 1)
For hot-gas defrost systems the compressor needs to be activated while defrosting. After
defrost the drip-off-time (P27) starts. During this time the defrost-relay and the compressor
are not active, so the cool-unit can drip-off.
Remark: The defrost-sensor is default not active (parameter P08=0) and
the defrost-mode is default set to natural-defrost (parameter P24=0) means
defrost-relay not active.
10 Alarm
As a failure or alarm occurs, an error messages is shown in the display. The ALFA(NET) 75 RTDF
remembers it’s error message, although it is already solved. The error message is resettable with
the SET key. As if after pressing the SET key (= reset alarm) the alarm still is not solved than the
ALFA(NET) 75 RTDF displays the temperature and the error message alternated. Is the alarm
solved, then the error message disappears and the temperature is displayed normally.
11 Error messages
In the display of the ALFA(NET) 51 PI the following error messages can appear:
Lo1 - Minimum alarm. Solution E1:
Hi1 - Maximum alarm. - Check if the sensor is connected correctly.
E 1 - Control Sensor failure. - Check sensor (1000Ω/25°C).
E 2 - Defrost Sensor failure - Replace sensor.
Reset Alarm. When a error-messages appears it can be resetted by pushing the SET key.
