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Active System Protection Features - Fujitsu FO20R Series Installation Instructions Manual

Variable speed r-410a heat pump outdoor units
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8.0 ACTIVE SYSTEM PROTECTION FEATURES

The controls found in the 20 SEER heat pumps
are designed to prevent the system from operating
in under conditions that could be harmful to the
compressor and inverter. The Variable Speed
Outdoor Control (VSODC) and Power Inverter
continuously monitor multiple sensors, current, and
voltage and will modify the compressor speed or
completely shut the system down to protect the
compressor and/or inverter if harmful operating
conditions are sensed. This process is called
Active System Protection. Sections 8.1 – 8.14
give a brief description of the different forms of
protection that are provided. Refer to Section 9.5
in the Diagnostic and Troubleshooting Section
of this manual for Active System Protection fault
codes and additional details for each fault.
8.1 Minimum Run Timer
A minimum run time of 30 seconds is maintained
by the VSODC to minimize short cycling which can
be harmful to the compressor.
8.2 Oil Return Cycle
When the system has been operating at
significantly reduced capacity for an extended
period of time, the Variable Speed Outdoor Control
(VSODC) will signal the Inverter to speed the
compressor up to 100% capacity to help bring any
oil that has accumulated in the indoor coil and
refrigerant lines back to the compressor sump.
8.3 Off-Cycle
Refrigerant Migration –
Stator Heat
Refrigerant can migrate to a cold compressor dur-
ing the off cycle which can dilute the oil or result
in the oil being pumped out when the compressor
starts. When needed, the VSODC will signal the
inverter to energize one of the compressor stator
windings (Stator Heat) to generate enough heat to
warm the compressor to prevent refrigerant migra-
tion to the compressor or boil off any refrigerant
that may have migrated to the compressor.
8.4 High Discharge
Temperature
The Power Inverter continuously monitors the
Discharge Line Thermistor input to protect the
compressor should the discharge temperature
reach an unsafe level. If the discharge line
temperature rises to 235°F [113ºC], the Inverter
will reduce the compressor RPM incrementally
until the temperature drops to 200°F [93ºC]. After
the discharge temperature reaches 200°F [93ºC],
40
the Inverter will gradually increase the compressor
RPM until the compressor returns to normal
speed based on the capacity demand. Should the
discharge temperature rise to 235°F [113ºC] again,
the Inverter to repeat the speed reduction cycle to
maintain a temperature below 235°F [113ºC].
8.5 High Discharge
Pressure
The High Pressure Control (HPC) limits the
compressor discharge pressure to a safe level
to prevent damage to the compressor. When
the HPC contacts open at 610 PSIG [4206 kPa],
the compressor will proceed to shut down and
restart per the sequence shown below. If the HPC
contacts open three (3) times during the same call
for operation, the VSODC will lock the compressor
out and will flash a 29L fault code and the Digital
Control Center will display a High Refrigerant
Pressure Lockout fault on the screen. A manual
reset is required for the VSODC to exit the
compressor lock-out mode and clear the fault. This
is accomplished by disconnecting the electrical
power to both the indoor and outdoor units for 1
minute and then reconnecting power.
NOTE: If the system experiences a high
refrigerant pressure lock-out, the system
should be evaluated to determine the cause
for the high pressure condition and corrective
action taken to eliminate the cause. Possible
causes include excessive refrigerant charge,
a failed indoor blower motor, dirty return air
filter, or a dirty indoor coil (heating mode) or
excessive refrigerant charge, a failed outdoor
motor, or dirty outdoor coil (cooling mode).
8.6 Low Suction Pressure/
Loss of Charge
The Variable Speed Outdoor Control (VSODC)
continuously monitors the Suction Pressure
Transducer input and will protect the compressor
from damage by shutting it down when the suction
pressure drops below 50 PSIG [345 kPa] in the
cooling mode and below 15 PSIG [103 kPa] in the
heating mode. A low pressure condition can result
from inadequate indoor air-flow, low refrigerant
charge, failed EXV, or a restriction in the refrigerant
circuit. The VSODC will allow the compressor to
restart if the suction pressure rises to 95 PSIG [655
kPa] in the cooling mode and 40 PSIG [276 kPa]
in the heating mode. A low refrigerant pressure
fault will be ignored for the first 90 seconds of
compressor operation and during the entire defrost
cycle to eliminate nuisance faults.

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