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Fujitsu FO20R Series Installation Instructions Manual page 38

Variable speed r-410a heat pump outdoor units
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7.0 COMPONENTS & CONTROLS
7.9 High Pressure
Control (HPC)
Sensing of the compressor discharge pressure is
accomplished by a conventional automatic reset
pressure control that is brazed into the compressor
discharge line. The HPC leads connect directly to
the inverter which communicates with the Variable
Speed Outdoor Control (VSODC). The contacts
on the high pressure control (HPC) open when the
compressor discharge pressure of approximately
610 PSIG [4206 kPa] and automatically close when
the pressure drops below approximately 420 PSIG
[2896 kPa].
7.10 Liquid Pressure
Transducer
20 SEER heat
pumps are equipped
with a liquid
pressure transducer
for the purpose of
measuring the liquid
pressure at the
outdoor unit. The
output of this device
is a 0.5 – 4.5VDC
signal that the
VSODC converts to
a pressure used for
calculating the liquid subcooling level. The VSODC
communicates the liquid pressure and subcooling
level to the Digital Control Center where they are
displayed on outdoor unit status screen.
7.11 Liquid Temperature
Thermistor
20 SEER heat pumps are equipped with a
liquid temperature thermistor for the purpose
of measuring the liquid line temperature at the
outdoor unit. The liquid line temperature is used
by the VSODC to calculate the cooling and
heating mode liquid subcooling level. The VSODC
communicates the liquid line temperature and
subcooling level to the Digital Control Center where
they are displayed on outdoor unit status screen.
MODEL
20
20
20
20
38
7.12 Outdoor Ambient
Temperature Sensor
The outdoor ambient temperature is sensed by a
thermistor located directly underneath the control
box where it is shielded from direct sunlight. The
thermistor leads plug into the connector marked
OAT on the Variable Speed Outdoor Control
(VSODC). The outdoor ambient temperature is
utilized by the VSODC and Digital Control Center
for several control functions and is displayed on the
Digital Control Center.
7.13 Outdoor Fan Motor
20 SEER heat pumps are equipped with variable
speed outdoor fans controlled by a pulse width
modulated signal (PWM) from the Variable Speed
Outdoor Control. The fan speed is selected to
optimize performance based on compressor speed.
7.14 Outdoor Fan Blade
20 SEER heat pumps are equipped with a swept
fan blade design that provides improved efficiency
and quieter operation than conventional fan blade
designs.
7.15 Power Inverter
Compressor Control
20 SEER heat pumps are equipped with a power
inverter that varies the compressor speed to match
the changing capacity needs of the conditioned
space. The inverter interfaces with the Variable
Speed Outdoor Control (VSODC) which communi-
cates the level of system capacity that is required
to the inverter based on input from the Digital
Control Center or conventional 24VAC 2-stage
thermostat. The inverter converts incoming single
phase power to simulated variable frequency
3-phase power that is connected to the 3-phase
compressor motor. Each of the four models has a
unique inverter specifically designed and qualified
for that specific model to provide reliable operation
under the most extreme conditions. Each inverter
is programmed to monitor compressor power
consumption, motor torque, input current, input
voltage, compressor discharge pressure, and com-
pressor discharge temperature. When the inverter
identifies a condition that could potentially result
in compressor or inverter damage, it automatically
reduces the compressor speed until a more reli-
able operating condition is obtained or shuts the
compressor completely off if necessary. Once
safe operating conditions are attained, the inverter
will gradually increase the compressor speed in
an attempt to meet the capacity demand as long

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