OM 1263 • MICROTECH UNIT CONTROLLER 44 www.DaikinApplied.com
Compressor Protection Unloading Control
There are a number unloading control functions that limit
the staging and speed control of the compressors to protect
them from damage under abnormal operating conditions. The
following unload functions are provided:
• Cooling High Pressure Unloading Control
• Cooling Low Pressure Unloading Control
• Heating High Pressure Unloading Control
• Heating High Protection Control [anticipating high
pressure]
• Heating Low Pressure Unloading Control
• Inverter Compressor High Discharge Line Temperature
Unloading Control
• Standard Compressor High Discharge Line Temperature
Unloading Control
• Inverter Compressor High Current Unloading Control
• Inverter Compressor Request for Unloading Control
• Compression Ratio Unloading Control
• Inverter Compressor Board Temperature Unloading
Control
• Low Dierential Pressure Protection Control
Cooling High Pressure Unloading Control
Normal compressor operation is limited during cooling operation
when high discharge pressure conditions occur. When the
discharge pressure rises above 503 psi the inverter compressor
is immediately reduced by three steps* and then reduced a
further step every 10 seconds in an attempt to keep the pressure
from rising above 515 psi. If reducing the compressor capacity
fails to keep the pressure below 515 psi the inverter compressor
is reduced to minimum and any xed speed compressor running
is stopped. If the discharge pressure continues to rise above 527
psi, compressor operation is forced to the Standby state where it
remains for a cooling stage time period before being allowed to
restart. If the unit is forced to Standby in this manner 3 times in
a 30 minute period, a high pressure alarm is generated requiring
manual reset.
Once active this limiting function remains active until the
discharge pressure falls back below 469 psi.
Cooling Low Pressure Unloading Control
Normal compressor operation is limited during cooling
operation when low suction pressure conditions occur. When
the suction pressure falls below 50 psi the inverter compressor
capacity is held at its current valve and the bypass solenoid
valve (SVB) is opened in an attempt to keep the pressure from
falling below 36 psi. If the pressure continues to fall below 36
psi the inverter compressor is slowed to minimum speed and
any xed speed compressor running is stopped. If the pressure
continues to fall below 10 psi, compressor operation is forced
to the Standby state where it remains for a cooling stage time
period before being allowed to restart. If the unit is forced to
Standby in this manner 3 times in a 30 minute period, a low
pressure alarm is generated requiring manual reset.
Once active this limiting function remains active until the
suction pressure rises back above 57 psi.
Heating High Pressure Unloading Control
Normal compressor operation is limited during heating
operation when high discharge pressure conditions occur.
When the discharge pressure rises above 481 psi the inverter
compressor capacity is immediately reduced by seven steps
and then reduced a further step every 10 seconds in an
attempt to keep the pressure from rising above 497 psi. If
the pressure continues to rise above 497 psi the inverter
compressor is slowed to minimum speed and any xed speed
compressor running is stopped. If the pressure continues to
rise above 527 psi, compressor operation is forced to the
Standby state where it remains for a heating stage time period
before being allowed to restart. If the unit is forced to Standby
in this manner 3 times in a 30 minute period, a high pressure
alarm is generated requiring manual reset.
Once active this limiting function remains active until the
discharge pressure falls back below 427 psi.
* See page 50 for more information about what is a
compressor “step”.
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