• 19 •CLIMATIC RT_UNITARY-IOM-1508-E
COMPONENTS
COIL DEFROST
Function
The CLIMATIC manages defrost procédure to avoid ice on the evaporator coil in heating mode (winter season).
Description
To avoid icing of the external air exchanger during winter operating, it’s necessary to reverse the refrigerant cycle. The dynamic defrost
allows the unit to start the defrost procédure only when the coil is frozen. This achieves through the measurement of the temperature
between the coil and the outside air.
The defrost procédure is activated if the following conditions are met during 1 minute:
• the outside air temperature is (3541),
• one of the compressor(s) on the circuit has been running for a time (3543) since the last defrost,
• the saturated temperature ratio is (3542).
The defrost procédure is characterized by the following steps:
1. start electrical heater during 2 min (rooftop with electrical heater only),
2. stop the compressors on the concerned circuit,
3. wait for 5 s
4. reverse the 4WV
5. start all compressors on the circuit (if the blowing T° is not too low),
6. start all condenser fans when the HP 50.0°C,
7. stop all condenser fans when the HP 42.0°C,
8. repeat the steps 6. to 7. N times (N is confi gurable in the menu (3544), 3 from factory setting)
9. stop the compressors of the circuit,
10. wait for 1 min to equalise the pressure in the circuit,
11. start the fans 30s to dry the condensenser
12. end of procedure; restart the unit in heating mode.
13. reverse the reversing valve after 5 s if P>2 bar.
In menu (3545), it is possible to start only one compressor per circuit with tandem during the defrost.
Temperature difference
between coil and outside
Time
Coil frozenCoil freezingCoil clean
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