Document Part # 026-4280 Rev 1 Page 15 of 33
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• Each time any of the LAN controller begins a defrost
cycle, it issues the command into the network making
all the other controllers start their own cycle. This
allows a perfect synchronization of the defrost in the
whole multiplexed cabinet according to the LMd
parameter.
• Selecting the dPA and dPb probes and by changing the
dtP and ddP parameters, the defrost can be started
when the difference between dPA and dPb probes is
lower than dtP for all ddP time. This is useful to start
defrost when a low thermal exchange is detected. If
[ddP = 0], this function is disabled.
12.5.2. Minimum Defrost Time
The “ndt” (0 to MnF) Minimum Defrost Time, set the
minimum defrost duration, when the defrost is ended by
evaporator temperature probe.
The ndt time is taken in account every time the defrost is
trigged, independently form the value of end defrost
temperature probe and end defrost digital input status.
12.5.3. Defrost Ending
• When defrost is started via rtC, the maximum defrost
duration is obtained from the Md parameter and the
defrost end temperature is obtained from the dtE
parameter (and dtS if two defrost probes are selected).
• If dPA and dPb are present and [d2P = Y], the device
stops the defrost procedure when dPA is higher than
dtE temperature and dPb is higher than dtS
temperature.
At the end of defrost, the drip time is controlled through the
Fdt parameter.
12.5.4. Kind of Defrost
The kind of defrost is set by parameter tdF among the
following possibilities.
tdF = Air: natural defrost. Defrost is made by opening the
compressor/solenoid relay. The fan during defrost
depends on the parameter Fnc. Defrost relay is off. The
valve is closed
tdF = EL: defrost with electrical heater: Defrost is made by
opening the compressor/solenoid relay. The fan during
defrost depends on the parameter Fnc. Defrost relay is
on. The valve is closed
tdF = in: hot gas defrost. Defrost is made by closing the
compressor/solenoid relay. The fan during defrost
depends on the parameter Fnc. Defrost relay is on. The
valve opening percentage during the defrost is set by
the par. oPd.
12.6. On Demand Defrost
12.6.1. Description
Controller can perform on demand defrost. It is based on the
behavior of evaporator temperature.
Controller monitors the evaporator temperature and triggers
a defrost if some conditions are satisfied. For defrost
efficiency it is important to place the “end defrost probe”,
usually P2, in the coldest place of the evaporator, usually
immediately after the expansion valve.
NOTE: Because of different type of evaporators and
consequentially behaviors, it is recommended to test and validate
this algorithm in a climatic chamber before applying it in the field.
12.6.2. Parameters and Settings
The «On Demand Defrost» can be activated with the following
settings:
CrE=”n”, EdF=”Aut”
cdt: evaporator temperature differential to trigger a
defrost (default cdt = 4°K)
nbd: minimum compressor run before automatic defrost
(or minimum time of activation of solenoid valve) it has to be
set properly. It prevents defrost from starting (default
nbd = 4.0 hours)
Mbd: max compressor run before automatic defrost (or
max time of activation of solenoid valve): it has to be set
properly. If reached a defrost is triggered (default
Mbd = 16.0 hours)
nct: minimum evap. temperature, it has to be set properly.
a defrost is triggered when this temperature reached (default
nct = -30°C)
NOTE: With CrE=”y” or CrE=”EUP” or CrE=EU5 only «RTC defrost»
and «interval defrost» are allowed. With EdF=”Aut” & CrE=”y” or
CrE=”EUP” or CrE=EU5 the «interval defrost» will be performed, as
with EdF = in
12.6.3. Exceptions
1. A defrost cannot be triggered if the compressor has not
ran more than minimum time (nbd parameter) since the
last defrost or initial power up. (Resolution hh.m)
2. If the compressor has ran for more than maximum time
since the last defrost or initial power up (Mbd parameter),
a defrost is triggered regardless of coil temperature.
3. If the coil temperature reaches very low temperature, (nct
parameter), a defrost is triggered regardless of cdt value.
12.7. Fans
12.7.1. Control with Relay
The fan control mode is selected by means of the FnC
parameter:
• C-n = running with the solenoid valve, OFF during
defrost
• C-Y = running with the solenoid valve, ON during
defrost
• O-n = continuous mode, OFF during defrost
• O-Y = continuous mode, ON during defrost
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