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ir33 +030220441 - rel. 2.0 - 01.05.2006
• immediate alarm from external digital input (A4, A5), as this delays compressor activation;
• alarm delayed by time (A7) from external digital input (A4, A5) as this delays compressor activation;
• high condenser temperature alarm (only with hot gas defrost), as this delays compressor activation
• opening the door (only with hot gas defrost if the compressor has the door management algorithm).
6.6.3 Starting the defrost
The defrost is performed by electric heater or hot gas, according to the value of parameter d0. If defrost
by temperature has been selected, the defrost is performed only if the evaporator probe reading is less
than the end defrost temperatures (dP1 and dP2), or if there is a probe error. This is also true in the case
of two evaporators.
For electric heater defrost:
• the compressor stops (pump down is run, if enabled);
• the time d3 elapses;
• the defrost relays for the main and second evaporators are activated, to start the heaters.
In hot gas defrost:
• the compressor starts;
• the time d3 elapses;
• the defrost relays for the main and second evaporators are activated to open the hot gas valve.
6.6.4 Defrost in progress
During the defrost procedure, the display is controlled according to the setting of parameter d6. If during
this procedure, the opening of the door is detected by the external digital contact, the compressor stops
(with the pump down procedure, if enabled). When the door closes, the compressor resumes the defrost
procedure, while the status of the fans is determined by setting of parameter F3. If defrost by temperature
is selected, the temperature thresholds deactivate the corresponding defrost relay when the temperature
exceeds the thresholds (‘dt1’,’dt2’) and activate the corresponding defrost relay when the temperature is
below the thresholds (‘dt1’,’dt2’) minus the fi xed hysteresis of 1°C.
Notes:
1. if the defrost probe is specifi ed for the second evaporator, but the second evaporator defrost output
is not used, the defrost on the second evaporator is performed using the output for the fi rst eva-
porator. In this case, if defrost by temperature is selected, the defrost relay is off if both evaporators
probes have exceeded the corresponding thresholds (‘dt1’,’dt2’).
2. if the defrost probe is not specifi ed for the second evaporator, but the second evaporator defrost
output is used, the defrost on the second evaporator is performed by time or considering the tempe-
rature of the fi rst evaporator.
6.6.5 End defrost
The defrost ends by temperature (dt1, dt2) or by time (dP1, dP2) according to the setting of parameter
d0. The defrost by temperature always ends after the set time (‘dP1’, ‘dP2’). If defrost by temperature is
selected, it may also end by timeout (dP1, dP2) and, in this case, according to the setting of parameter
A8, signal Ed1 or Ed2 is displayed. In the case of an error in the probe selected for the defrost (main or
auxiliary evaporator), it is always performed by time, with the timeout signal if enabled (Ed1 or Ed2). In
the case of two evaporators, the defrost ends when both the evaporators have reached the end defrost
condition. If one evaporator fi nishes the defrost (by time or by temperature) before the other, the
corresponding defrost relay is de-energised, while the compressor remains in the status required by the
defrost.
The defrost is ended early in the following situations:
• changeover from Direct operating mode with defrost to Reverse-cycle mode (heating), by parameter
(r3) or the digital input (A4, A5);
• end of enabling signal from external digital contact (the defrost request remains pending);
• instrument switched OFF from the keypad, supervisor and digital input;
• end defrost from supervisor and keypad.
If the defrost is completed early, the dripping and post-dripping (with the fans OFF) phases are not
performed, as if the times were 0.
Special case: if the controller is running a hot gas defrost and a low pressure alarm occurs, the compres-
sor will stop due to the low pressure alarm, and the defrost will probably end by timeout. At the end of
the defrost:
• the compressor is stopped (hot gas) and pump down is run (if enabled), if a dripping time is set (dd);
• the fans are stopped, if a dripping time (dd) or fans off for post-dripping (Fd) is set;
• the defrost relay is disabled;
• the alarm bypass time after defrost is activated (d8);
• any pending defrost requests are reset.
If the dripping time is set to zero, the compressor remains in the previous status, and normal control resu-
mes directly. If the dripping and post-dripping times are set to zero, the compressor and the fans remain in
the previous status, and normal control resumes.
6.6.6 End multiplexed defrost
The multiplexed defrost occurs:
• on the master ‘In’=1 following each event able to activate the defrost,
• on the slaves ‘In’=2 to 6 following a defrost signal from the supervisor.
In the case of multiplexed defrosts, the end defrost conditions described in the previous point are still valid,
however before going to dripping the master and slave wait for the signal from the network synchronizer. In
any case, the defrost will end by timeout.
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