Daikin MicroTech III Operation Manuals page 119

If the oil balance mode fails to resolve the low oil condition,
or the fixed speed compressor was not running when the low
oil indication occurred, or the VFD compressor was not part
of a tandemized compressor set, when the low oil indication
occurred, the unit will enter boost mode
Upon entering oil boost mode, the VFD compressor speed is
increased to the oil boost value shown in Table 20 . If the VFD
compressor is part of a tandem arrangement, the fixed speed
compressor is started as well . The VFD compressor runs
at this condition until the optical oil sensor verifies that oil is
present for 3 continuous minutes . Unit Controller default is set
for a 10 minute max boost .
During the oil balance/boost sequence the DAT temperature is
overridden to allow the VFD compressor to continue operating
until oil balance/boost sequence termination .
If one or more fixed speed compressors on the non VFD
compressor circuit is operating, and the fixed speed
compressor on the VFD compressor circuit was not already
running when entering the oil boost mode, one fixed speed
compressor on the non VFD compressor circuit will be turned
off to minimize the disturbance to the DAT .
Oil balance/boost sequences and durations are logged in the
unit controller .
If low oil indication does not clear, the VFD compressor will be
shut down and oil level will be monitored for an additional 15
minutes . If low oil indication still does not clear within these 15
minutes, the VFD compressor will be locked out on alarm .
The low oil problem is also generated and the VFD compressor
circuit is disabled if the oil boost sequence is initiated more
than 4 times in a 24 hour period . If the oil balance/boost
sequence successfully restores the VFD compressor oil level
the fixed compressor stage is returned to its pre-oil balance/
boost condition and normal compressor sequencing and
modulation resumes
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VFD Compressor Protection Unloading Control
There are several modulating control functions that adjust the
speed control range of the VFD compressor to protect it from
damage under abnormal operating conditions . The following
functions are provided by the unit controller
• High Pressure Unloading Control
• High Discharge Line Temperature Unloading Control
• High/Low Discharge Superheat Control
• Condenser Coil Splitter Valve Control (For Low Ambient
Option)
High Pressure Unloading Control
The VFD compressor has an upper operating sat discharge
pressure limit of 575 PSIG . If the discharge pressure exceeds
575 PSIG, the compressor speed is reduced 1 rps every 10
seconds until the discharge pressure is at or below 575 psig .
If the discharge pressure does not drop below 575 PSIG with
the VFD compressor operating at minimum speed (30 rps), the
compressor is locked out on alarm .
In addition, when the VFD compressor is operating above a
sat discharge pressure of 525 PSIG, the VFD compressor
maximum speed is limited to 90 rps and the minimum speed is
limited to 30 rps .
A high side pressure transducer is standard on the VFD circuit
allowing the discharge pressure of the refrigerant circuit to be
viewed at the unit controller display .
If the unit controller needs to reduce the compressor speed in
order to limit discharge pressure, the action is recorded in unit
controller event log section .
119 OM 920-6 • MICROTECH UNIT CONTROLLER
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