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Demand Limit Control Option — the demand limit control option (4-20 mA DEMAND LIMIT TYPE) is
externally controlled by a 4 to 20 mA signal. The option is set up on the CONFIGURATION
MENU/GENERAL CONFIGURATION screen. When enabled, 4 mA will set ACTIVE DEMAND LIMIT to
100% of the DEMAND LIMIT SOURCE (regardless of the value of BASE DEMAND LIMIT), and 20 mA
will set ACTIVE DEMAND LIMIT to the value configured as “DEMAND LIMIT AT 20 mA” in the
CONFIGURATION MENU/SERVICE PARAMETERS screen.
5.15. Override Control
Capacity overrides can prevent some safety shutdowns caused by exceeding the motor amperage limit,
evaporator refrigerant low temperature safety limit, motor high temperature safety limit, and condenser
high pressure limit. In all cases there are 2 stages of capacity control.
- When the value of interest crosses the First Stage Set Point into the Override Region, the capacity
are prevented from increasing further, and the status line on the 19 Series Carrier® SmartVu
TM
controller indicates the reason for the override. Normal capacity control operation is restored when
the value crosses back over the First Stage Set Point, leaving the Override Region.
- When the value of interest is in the Override Region and further crosses the Second Stage Set
Point, the capacity shall be decreased until the value meets the Override Termination Condition.
The 19 Series Carrier® SmartVu
TM
controls resume normal capacity control operation after the
override termination condition has been satisfied. (In the case of high discharge superheat, there
is an intermediate stage.)
Besides the above overrides, other types of override will not override control guide vane or VFD.
Only override events are reported.
High Compressor Discharge Temperature Override
If the COMP DISCHARGE TEMP is greater than the COMP DISCHARGE ALERT threshold then
high discharge temperature override will be displayed in the main screen until the COMP DISCHARGE
TEMP is less than the COMP DISCHARGE ALERT threshold – 2F.
High Compressor Bearing Temperature Override
For 19XR6/7 and 19DV, if one of the compressor bearing temperature is greater than the
compressor bearing temperature Alert threshold then High Bearing Temperature Override will be active
until all of the compressor bearing temperature is less than Comp Bearing Temp Alert minus 2F.
For 19XR2~5/C/D/E/V/F chiller, if the calculated bearing temperature is greater than the bearing
temperature alert threshold, then high bearing temperature override will be active until the calculated
bearing temperature is less than the threshold minus 2F.
Low Discharge Superheat Temperature Override
Ignore low discharge superheat override during first 5 minutes after chiller startup completed. After 5
minutes elapse, for two stage 19XRE/F/C chiller, keep ignoring it until the first time (Cond pressure –
Evap pressure)>10psid; for 19XR6/7, keep ignoring it until the first time Damper becomes not fully
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