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8.0 ACTIVE SYSTEM PROTECTION FEATURES
System Protection
The controls found in the (-)P17 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 – 8.15
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 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
compressor 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 compres-
sor starts. The VSODC continuously monitors the
Compressor Sump Thermistor input during the
off-cycle and when the compressor shell tempera-
ture 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
