Inverter Compressor High Board
Temperature Unloading Control
Normal compressor operation is limited when inverter
compressor control board indicates an abnormally high board
(n) temperature value. This indicates the inverter compressor
board is not receiving problem ventilation. When the inverter
board temperature exceeds 183°F (460/575V unit) or 178°F
(208/230V unit), the inverter compressor is immediately
reduced by one step then reduced a further step every 15
seconds in an attempt to keep the board temperature from
continuing to increase. The outdoor fan(s) are increased to
maximum speed.
Once active this limiting function remains active until the
inverter board temperature falls 5.4°F below the high limit.
Low Differential Pressure Protection
Control
Normal compressor operation is overridden when the
differential pressure between the high and low side of the
refrigeration circuit (PTD-PTS) is abnormally low. This
condition can inhibit proper oil return for lubricating the inverter
compressor. When the differential pressure falls below 85 psi
continuously for 40 seconds, the inverter compressor capacity
is increased by one step then increased a further step every 40
seconds in an attempt to increase the differential pressure. If
the inverter compressor is at maximum speed for 40 seconds
and the differential pressure is still below 85 psi, compressor
operation is forced to the Standby state where it remains for a
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 differential pressure alarm is generated requiring manual
reset.
Once active this limiting function remains active until the
differential pressure rises back above 171 psi.
To prevent excessive cycling of the compressor heating on an
off during moderate heating load conditions, special steps are
taken if this protection function causes the unit to cycle out of
heating while it is active. If this occurs, the current effective
compressor heating ambient lock out setting is reduced 10°F
below the current outdoor air temperature which will lock out
compressor heating operation. The effective compressor
heating ambient lock out setting remains at this lower value
until any of the following occur:
120 minutes elapses
The effective minimum outdoor damper position changes by
more that 10%.
The effective discharge air heating set point changes by more
than 5°F.
e outdoor air temperature falls below this lower eective
compressor heating ambient lock out setting.
coMpressor protectIon
www.DaikinApplied.com 81 OM 1141-3 • MICROTECH UNIT CONTROLLER
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