4–19 62-12259
10. Low Suction Pressure Override
If suction pressure is below -4 psig (-.27 bar) for > 20 seconds , inhibit high speed operation. Remain in low
speed for five minutes and until the suction pressure > -3 psig (-.2 bar).
11. Perishable S/S High Speed Override
With the system running in Start-Stop Run, Perishable mode, the safety conditions and minimum on time
are met, but the temperature condition is not met, run in high speed. Remain in high speed until the engine
shuts off or the safety conditions are no longer met.
12. High Speed Pulldown
for perishable continuous run mode, if High Speed Pulldown is active, remain in high speed until termination
conditions have been met.
13. Product Shield High Air
The engine is forced to high speed if the PRODUCT SHIELD HIGH AIR Configuration is active, refer to
Section 4.9.3
14. Range Protect
When the unit is operating in Range Protect and the compartment temperature is inside the protected
range, while all other conditions to allow an off cycle are not met the engine will operate in low speed.
4.10.4 CSMV Control Overrides
1. .Engine RPM
When the engine throttle position has been more than 90% for three seconds the control system will moni-
tor 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 posi-
tion as required to eliminate the droop by lowering the load on the engine.
2. High Generator Current
If the system is operating with high generator current the microprocessor will throttle the compressor suc-
tion modulating valve (CSMV) in an attempt to reduce the load. If additional current reduction is required
the microprocessor 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 provide maxi-
mum allowable capacity. This action is called “staging”.
3. Discharge Pressure Control
The control system monitors the discharge pressure. When the pressure is above the calculated maxi-
mum, the CSMV will move toward the closed position as required to reduce the pressure.
4. Low Suction Pressure Control
The control system monitors the suction pressure. When the pressure is below the calculated minimum (-2
psig) the CSMV will move toward the open position as required to raise the pressure.
5. Compression Ratio
The microprocessor monitors compressor operating pressures and calculates a compression ratio. The
control system will open the CSMV to maintain the Maximum Compression Ratio.
To Next Page
Loading...
