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Application Guidelines
Running the compressor for a short period of time in reverse direction will have no negative impact but prolonged
running in reverse direction may cause premature failure. To reverse the rotation of a three-phase scroll compressor,
shut off the incoming power supply to the unit, swap connection of any two of the three incoming phases at the unit's
terminal block, reapply power to the unit and following compressor restart, recheck operating pressures.
For three phase systems, reverse rotation module in the system control unit is recommended in preventing three
phases compressor from running in the reverse rotational direction.
Voltage Imbalance
When the compressor is starting, the high starting current will cause drop of voltage. There is a possibility that
compressor fail to start if the starting voltage is too low. Thus, each phase voltage measured at the terminal of three
phase scroll/rotary compressor should be ±2% of the average of all phases.
Overload and Overheating Protection
For rotary 3 phase compressor: the compressor is protected by internal thermostat with specification (cut out =
110±4⁰C, cut in = 95±5⁰C). The internal thermostat connected to external overload protector, to disconnect all three
phases at contactor in case of overtemperature and overcurrent.
Overheating could be due to compressor working at high compression ratio (low evaporating and high condensing
pressure); loss/ inadequate charge; or condenser fan not working. Time must be allowed for the compressor to cool
down before the thermostat to reset.
For scroll compressor, an internal line break motor protector is located at the center of the Y of the motor windings
(motor located in low pressure dome), to disconnect all three phases in case overcurrent or overtemperature condition.
The protector is the automatic reset device containing snap action bimetal switch which reacts to a combination of
motor current and motor windings temperature. When internal motor protector has tripped, it will take 30 to 40
minutes to reset and then the compressor will restart.
On a field application, when the internal motor protector has tripped, the compressor will stop while each of 3
terminals is still energized, to which either the customer or serviceman may regard the compressor as fail down.
Therefore, the above-mentioned situation should be taken into consideration.
Over Pressure Protection
All Daikin condensing units are fitted with adjustable auto reset low pressure switch and manual reset cartridge type
high pressure switch.
Low Pressure Switch
The low-pressure safety switch protects the compressor against deep vacuum operation or loss of refrigerant
conditions, to avoid internal arcing at the electric terminal and the damage of compressor.
When low pressure occurs outside of compressor limit, the temperature in the compressor motor will rise rapidly.
Sometimes, the low-pressure switch will react in priority to the action of the discharge thermostat or motor internal
protector when huge amounts of refrigerant leaks in short time.
T-CU11-OCT22-0
Page 9
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