Daikin DPS Installation And Maintenance Manual page 80

Heating High Pressure Protection
Control
Normal compressor operation is limited during heating operation
when high discharge pressure or high inverter compressor
discharge line temperature conditions occur while the inverter
compressor is operating alone (fixed speed compressor off or
not present) at low speed . This is an indication that too much
liquid is backing up in the condenser causing hot high pressure
conditions . When the DRT1 sensor input rises above 234°F or
the discharge pressure rises above 455 psi while the inverter
compressor is operating alone at low speed, the inverter
compressor capacity is immediately reduced to minimum speed
and the indoor expansion valve (EVI) is driven fully open . Note
the bypass solenoid valve is also opened if DRT1 is above
234°F or if the pressure is above 469 psi .
Once active this limiting function remains active until the discharge
pressure falls back below 427 psi, DRT1 is below 225°F and
Heating High Pressure Unloading is inactive .
Heating Low Pressure Unloading
Control
Normal compressor operation is limited during heating operation
when low suction pressure conditions occur . When the suction
pressure falls below 24 psi the inverter compressor is reduced
by three steps then reduced a further step every 10 seconds in
order to keep the pressure from falling below 19 psi . If reducing
the compressor capacity fails to keep the pressure above 19 psi,
the inverter compressor is reduced to minimum and any fixed
speed compressor running is stopped . If the suction pressure
continues to fall below 10 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 low
pressure alarm is generated requiring manual reset .
Once active this limiting function remains active until the suction
pressure rises back above 33 psi .
Inverter Compressor High Discharge
Line Temperature Unloading Control
Normal compressor operation is limited when high inverter
compressor discharge line temperature (DRT1) conditions
occur . When DRT1 rises above 239°F or a calculated suction
port temperature (Tp) value rises above 275°F, the inverter
compressor capacity is immediately reduced by one step and
then reduced a further step every 30 seconds in an attempt to
keep the temperatures from rising further . If DRT1 continues to
rise above 266°F or above 248°F continuously for 90 seconds,
the inverter compressor is reduced to minimum and any
operating fixed speed compressor is stopped. If DRT1 continues
to rise above 275°F or above 248°F continuously for 10 minutes
or Tp rises above 302°F, 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 100 minute period, a high inverter discharge
line temperature alarm is generated requiring manual reset .
Once active this limiting function remains active until DRT1 falls
back below 212°F and Tp is below 230°F .
OM 1141-3 • MICROTECH UNIT CONTROLLER
Fixed Speed Compressor High
Discharge Line Temperature Unloading
Control
Normal fixed speed compressor operation is limited when high
discharge line temperature (DRT3) conditions occur . When
DRT3 rises above 275°F or above 248°F continuously for 5
minutes or when a calculated inverter compressor suction port
temperature (Tp) value rises above 293°F or above 275°F
continuously for 10 minutes, the fixed is stopped.
Once active this limiting function remains active for 10 minutes .
Inverter Compressor High Current
Unloading Control
Normal compressor operation is limited when high inverter
compressor current conditions occur . When the internal inverter
compressor amp draw exceeds 14 .7A (460/575V unit) or 26 .5A
(208/230V unit) the inverter compressor capacity is immediately
reduced by one step and then reduced a further step every 15
seconds in an attempt to keep the amps below these values .
Once active this limiting function remains active until the amps
are above these values and the inverter capacity is back to the
normal unlimited value .
Inverter Compressor Request for
Unloading Control
Normal compressor operation is limited when inverter
compressor control board provides a request to unload . This
can occur for a number of internal compressor board built-in
protection reasons (high amp draw for example) . When the
inverter unload request is active, the inverter compressor
capacity is immediately reduced by one step and then reduced
a further step every 15 seconds as long as the request remains
active .
Once active this limiting function remains active until the request
becomes inactive and the inverter capacity is back to the normal
unlimited value .
High Compression Ratio Unloading
Control
Normal compressor operation is limited when the ratio between
the compression ratio between the discharge and suction
pressure becomes too high . CmpRatio=(PTD + 14 .7)/(PTS +
14 .7) . Note: in this equation PTD and PTS are in PSI . When
the compression ratio exceeds 8 .5 the inverter compressor is
immediately reduced by three steps then reduced a further step
every 10 seconds in an attempt to keep the compression ration
from continuing to increase . If the compression ratio continues to
rise above 8 .9, the inverter compressor is reduced to minimum
and any operating fixed speed compressor is stopped.
Once active this limiting function remains active until the
compression ratio falls back below 8 .0 .
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