MAINTENANCE AND OPERATING MANUAL
Electronic controller
HAS T 070÷140
73
ENGLISH
EN
The data in this manual are not binding and they can be modified by the manufacturer without notice. Reproduction of this manual is strictly prohibited.
6.7.9.1Defrost conditions
The formation of ice on a coil causes a reduction of efficiency of the corresponding circuit. This can be detected by an
excessive increase in the maximum difference of real temperature MTDR compared to the target temperature MTDI or an
excessive lowering of the evaporation pressure.
From the display you can select the real MTD coefficient calculation probe of each circuit and the setting for the condition:
MTDR >
MTDI + SET
which, if true, starts the defrost procedure after an activation time lag.
The procedure is activated also in the event in which evaporation pressure of the circuit is below a setpoint defined after an
activation time lag. The condition is false if the pressure becomes greater than setpoint+diff.
6.7.9.2Defrost procedure
If one of the two defrost conditions is confirmed on a circuit, the following procedure is activated:
1. Inversion of cycle valve: the compressors react in accordance with the cycle valve inversion type defined. Valve
inversion is carried out after a time lag;
2. Activation of all compressors of the circuit after a time lag. The compressors are started, one after the other, with
a parametrizable time interval, and the relative fans are started for a time having the same duration as the defrost
procedure.
3. Dripping: the compressors behave in accordance with the programmed type of valve inversion and the cycle valve
is inverted after the same time lag as in the first stage. After the cycle inversion, a dripping time is observed
before the end of the defrost procedure.
During the defrost cycle the fans are started after a time lag with respect to starting of the compressors, and they are
controlled in accordance with the settings of the low-noise procedure for chiller operation.
The period of exclusion is the minimum time that must elapse between two defrost procedures on the same circuit. The same
time is observed at each fresh activation of the circuit. The defrost procedure performed in accordance with the pressure
value does not observe the exclusion time.
The cycle valve inversion type can be:
• OFF COMP.: the compressors are all off during valve inversion;
• COMP. REG.: the compressors maintain their status during valve inversion;
• CIRC. CAP. CNTRL..: if completely activated, the circuit capacity is reduced by decreasing the number of
active compressors, during valve inversion.
6.7.10 Operating hours
The menu shows the operating hours and the number of starts of the unit's main devices. If the operating hours of a
device exceed the threshold set for maintenance, a warning is shown on the display.
The menu is accessible only via the service level password.
Exclusively for compressors, the following information is calculated and shown on the display:
• Number of starts of each compressor
• Maximum number of starts per hour for each compressor
• Average number of starts per hour for each compressor
• Minimum number of starts per hour for each compressor
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