37
System Protection
8.0 ACTIVE SYSTEM PROTECTION FEATURES
The controls found in the (-)A20 condensing units
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 – 8.15
give a brief description of the different forms of
protection that are provided. Refer to Section 9.4
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 help bring any oil that has
accumulated in the indoor coil and refrigerant lines
back to the compressor sump.
8.3 Oil Dilution
During operation, it is possible for excess
refrigerant to collect in the compressor causing
a flooded compressor sump which can dilute the
oil and harm the bearings inside the compressor.
The Compressor Sump Thermistor is continuously
monitored by the Variable Speed Outdoor Control
(VSODC). The VSODC will evaluate the differential
between the sump temperature and the saturated
suction temperature (sump superheat) and signal
the Inverter to reduce the compressor speed to
increase the sump superheat level should it fall
below a safe level. Once the minimum acceptable
sump superheat level is attained, the VSODU
will signal the Inverter to gradually increase the com
-
pressor speed as much as possible while
maintaining an acceptable sump superheat level
until the compressor speed returns to normal
speed based on the capacity demand.
8.4 Off-Cycle
Refrigerant Migration -
Stator Heat
Refrigerant can migrate to a cold compressor during
the off cycle which can dilute the oil or result
in the oil being pumped out when the compressor
starts. The VSODC continuously monitors the
Compressor Sump Thermistor input during the off-
cycle and when the compressor shell temperature
drops to 45°F [7.2°C], 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
migration to the compressor or boil off any refrig
-
erant that may have migrated to the compressor. If
Stator Heat is energized in the off cycle,
the compressor is prevented from starting until the
compressor shell temperature measured by the
Sump Temperature Thermistor is greater than 50°F
[10°C].
8.5 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],
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].
8.6 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, 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 EcoNet
TM
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
