User manual

47
ENG
MPXPRO - + 0300055EN rel. 1.3 07/03/13
6.7 Defrost
The advanced parameters for defrost management include general
parameters on the time base, activation delays, synchronization between
Master and Slaves, the stages of the defrost such as pump down and
dripping, and the advanced defrost functions, such as:
• Skip defrost;
• Running time;
• Sequential stops;
• Power defrost.
End defrost synchronized by Master (parameter d2)
Par. Description Def Min Max UoM
d2 End defrost synchronized by Master
0 = not synchronized;1 = synchronized
101-
Tab. 6.z
The parameter determines whether or not, in a local network, MPXPRO
awaits an end defrost signal from the Master at the end of the defrost.
End defrost signal by timeout (parameter r3)
Par. Description Def Min Max UoM
r3 End defrost signal by timeout
0 = disabled, 1 = enabled
001-
Tab. 6.aa
For defrosts that end by temperature (d0=0, 1, 5) , this enables the end
defrost by timeout signals Ed1 and Ed2.
Defrost on power-up (parameter d4)
Par. Description Def Min Max UoM
d4 Defrost on power-up
0= disabled ; 1 = enabled
(Master = network defrost;
Slave = local defrost)
001-
Tab. 6.ab
The defrost call on power-up has priority over the control request and the
activation of the continuous cycle. For Master controllers, the defrost on
power-up will be a network defrost; for Slave controllers it will be local.
Defrost delay on power-up (parameter d5)
Par. Description Def Min Max UoM
d5 Defrost delay on power-up (if d4=1)
0 = delay disabled
0 0 240 min
Tab. 6.ac
Also active when d4=0. If the digital input is set to enable or start a defrost
from an external contact, parameter d5 represents the delay between
when the defrost is enabled or called, and when it eff ectively starts.
For Mater/Slave networks where the defrost needs to be activated from
a digital input on the Master, use parameter d5 to delay the various
defrosts, thus avoiding current overloads.
Note: to avoid unwanted defrosts controlled by the controller
timer, set parameter dI=0 (defrosts from keypad, RTC, compressor
running time or digital input only).
Time base for defrost (parameter dC)
Par. Description Def Min Max UoM
dC Time base for defrost
0=dI in hours, dP1, dP2 and ddP in minutes;
1= dI in minutes, dP1, dP2 and ddP in
seconds
001-
Tab. 6.ad
This defi nes the unit of measure used to count the times for parameters
dI (defrost interval), dP1, dP2 and ddP (defrost duration):
• dC=0 =>dI expressed in hours, dP1, dP2 and ddP in minutes;
• dC=1 =>dI expressed in minutes, dP1, dP2 and ddP in seconds.
Note: parameter dC=1 can be useful for quickly testing the defrost
operation with reduced times. It is also useful for controlling the
operation of air dryers. The defrost cycle thus becomes the condensate
discharge cycle, which needs to be started at short intervals (minutes)
and for very brief periods (seconds).
Dripping time after defrost (parameter dd)
Par. Description Def Min Max UoM
dd Dripping time after defrost (fans off )
0 = no dripping
2 0 15 min
Tab. 6.baTab. 6.g.f
This parameter is used to stop the compressor and the evaporator fans
following a defrost so as to allow the evaporator to drip. The value of the
parameter indicates the off time in minutes. If dd=0 no dripping time
is enabled, and at the end of the defrost control resumes immediately,
without stopping the compressor and the fan, if active.
Pump down phase duration
Par. Description Def Min Max UoM
dH1 Pump down phase duration
0 = pump down disabled
0 0 999 s
Tab. 6.ae
The pump down phase is the period in which the evaporator is emptied
of liquid refrigerant. Parameter dH1 defi nes the duration of the pump
down phase during all types of defrost, heater or hot gas. Setting dH1=0
disables the pump down phase.
Important: the controller does not have two separate outputs to
manage the compressor and solenoid valve.
Type of multiplexed hot gas defrost
Par. Description Def Min Max UoM
dHG Type of hot gas defrost
0 = equalizing valve normally closed
1 = equalizing valve normally open
001-
Tab. 6.af
See paragraph 5.6 for an installation diagram with equalizing valve.
Located in parallel with the suction valve, it can be open only in the
dripping phase or also during the normal refrigeration cycle, the pump
down and post-dripping phases.
Defrost Running time (parameters d10, d11)
Running time is a special function that determines when the refrigeration
unit needs defrosting. In particular, it is assumed that if the evaporator
temperature measured by probe Sd remains continuously below a
certain set threshold (d11) for a certain time (d10), the evaporator may
be frozen and a defrost is activated. The time is reset if the temperature
returns above the threshold.
Par. Description Def Min Max UoM
d10 Defrost time in “Running time” mode
0 = function disabled
0 0 240 min
d11 Defrost temperature threshold in “Running
time” mode
-30 -50 50 °C/°F
dt1 End defrost temperature (read by Sd) 8 -50.0 50.0 °C/°F
dt2 End defrost temperature (read by Sd2) 8 -50.0 50.0 °C/°F
Tab. 6.ag
d10
t
t
ON
Sd
DEF
OFF
d1
d11
Fig. 6.l
Key
Sd Defrost probe t Time
DEF Defrost