Carrier TRANSICOLD Vector 8500, Operation & Service Manual

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4.11.4 CSMV Control Overrides
1. Engine Rack (Throttle) Position Limit
The control system monitors the engine throttle
position reading provided by the ENCU rack
position sensor (RPS). If the position is greater
than or equal to the maximum position (config-
uration parameter) the CSMV will move toward
the closed position as required to lower the
engine load, and thereby, the rack position.
2. Engine RPM
When the engine throttle position has been
more than 90% for three seconds the control
system will monitor actual engine RPM verses
desired engine RPM (if the actual RPM is less
than the desired RPM, this is defined as
engine RPM droop.) If the droop is above 10
RPM, the CSMV will move toward the closed
position as required to eliminate the droop by
lowering the load on the engine.
3. High Generator Current
If the system is operating with high generator
current the microprocessor will throttle the
compressor suction modulating valve (CSMV)
in an attempt to reduce the load. If additional
current reduction is required the microproces-
sor will transition from Economized Mode to
Standard Mode as required to prevent the
engine from stalling. As current is reduced, the
microprocessor will reverse these steps to pro-
vide maximum allowable capacity. This action
is called “staging”.
4. Discharge Pressure Control
The control system monitors the discharge
pressure. When the pressure is above the cal-
culated maximum, the CSMV will move toward
the closed position as required to reduce the
pressure.
5. Low Suction Pressure Control
The control system monitors the suction pres-
sure. When the pressure is below the calcu-
lated minimum (
− 2 psig) the CSMV will move
toward the open position as required to raise
the pressure.
6. Compression Ratio
The microprocessor monitors compressor
operating pressures and calculates a compres-
sion ratio. The control system will open the
CSMV to maintain the Maximum Compression
Ratio.