Daikin MicroTech III DPS Installation And Maintenance Manual page 46

Inverter Compressor High Board Temperature
Unloading Control
Normal compressor operation is limited when inverter
compressor control board indicates an abnormally high board
(fin) 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 .
OM 1263 • MICROTECH UNIT CONTROLLER
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 .
• The outdoor air temperature falls below this lower
effective compressor heating ambient lock out setting.
46
Compressor Protection
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