IM 893-10 • ROOFPAK SINGLEZONE UNITS 96 www.DaikinApplied.com
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Oil Boost Operational Sequence
When a low oil level is indicated in the VFD compressor sump,
the unit switches to an oil boost state. The VFD compressor
speed is increased during this mode to promote the return of
refrigerant oil to the compressor.
To avoid short cycling of the oil boost sequence, no action
is taken until a low oil indication has been present for 15
consecutive run minutes.
Upon entering oil boost sequence, the VFD compressor speed
is increased to 70 rps. 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 boost sequence the DAT temperature is
overridden to allow the VFD compressor to continue operating
until oil boost sequence termination.
If the VFD compressor is operating at or above 70 rps when
an oil boost sequence is demanded, the VFD compressor is
increased to the maximum allowable speed.
If one or more fixed speed compressors are operating in circuit
#1 when the oil boost sequence is initiated, one fixed speed
compressor will be turned off to minimize the disturbance to the
DAT.
Oil boost sequences and durations are logged in the unit
controller.
If the oil boost sequence runs for 15 continuous minutes
(default setting) and cannot satisfy the oil optical sensor, the
VFD compressor is operated for an additional 10 minutes at
maximum allowable speed.
NOTE:
See VFD Compressor Modulation Ranges Table on
for details.
If low 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 boost sequence
successfully restores the VFD compressor oil level the fixed
compressor stage is returned to its pre-oil boost condition and
normal compressor sequencing and modulation resumes.
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
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 both the VFD
and fixed speed circuits allowing the discharge pressure of both
refrigerant circuits 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
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