Carrier AquaEdge 19DV Controls Operation And Troubleshooting page 20

DEMAND LIMIT
The PIC6 controls provide a feature for limiting AVERAGE
LOAD CURRENT or MOTOR KILOWATTS by limiting ca-
pacity via guide vane control/VFD control. The limit may be
applied in two ways. The first is called ACTIVE DEMAND
LIMIT, which is equal to a BASE DEMAND LIMIT value (set
in the SETPOINT screen, default value 100%). ACTIVE DE-
MAND LIMIT may also be forced to be different from BASE
DEMAND LIMIT by manually overriding (forcing) the value
via a CCN network device. If the DEMAND LIMIT SOURCE
exceeds the ACTIVE DEMAND LIMIT by 5% or less, capaci-
ty will be inhibited. If the DEMAND LIMIT SOURCE ex-
ceeds the ACTIVE DEMAND LIMIT by more than 5%, ca-
pacity will be decreased.
Alternatively, the limit may be applied by AUTO DEMAND
LIMIT INPUT, an optional 4 to 20 mA input. This demand
limit control option (4 to 20 mA DEMAND LIMIT TYPE) is
externally controlled by a 4 to 20 mA signal. The option is set
up on the Configuration Menu
TION screen. When enabled, 4 mA will set ACTIVE DE-
MAND 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 config-
ured for DEMAND LIMIT AT 20 mA in the Configuration

Menu SERVICE PARAMETERS screen.
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 these cases there
are two stages of capacity control:
OVERRIDE CONDITION
High condenser pressure over-
ride (Unit Type Heat/Cool=1 in

Configuration Menu Factory.
Before configuring Unit Type = 1
verify that unit is able to withstand
pressure - note all North America
units are of 72 PSI design.)
High compressor discharge
temperature
High compressor bearing
temperature
Low evaporator temperature
override
High motor temperature override
Rectifier Overload (32VS VFD
only)
High current override
Low discharge superheat override
Low source temperature protec-
tion override

GENERAL CONFIGURA-
Table 14 — Override Parameters
FIRST STAGE
OVERRIDE PARAMETER
CAPACITY INHIBIT
CONDENSER > COND PRESS
PRESSURE OVERRIDE HIGH
COMP DISCHARGE TEMP >COMP DIS-
CHARGE ALERT
COMP BEARING TEMP >COMP BEARING
TEMP ALERT DV
CALC EVAP SAT TEMP < EVAP SAT OVER-
or RIDE TEMP (EVAP
EVAP REFRIG LIQUID SAT OVERRIDE
TEMP TEMP = EVAP TRIP-
POINT + EVAP
OVERRIDE DELTA T)
COMP MOTOR WINDING > COMP MOTOR
TEMP TEMP OVERRIDE
RECTIFIER OVERLOAD >100%
PERCENT LINE PERCENT LINE
CURRENT CURRENT > 100%
Discharge Superheat (DSH) < DSH REQUIRED + 1
Leaving water temperature < LWT PROTEC-
(heating mode) TION SETPOINT –
2°F (1.1°C)
1. When the value of interest crosses the first stage set point
into the override region, the capacity is prevented from
increasing further, and the status line on the PIC6 control-
ler 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.
2. When the value of interest is in the override region and
further crosses the second stage set point, the capacity is
decreased until the value meets the override termination
condition. The PIC6 controls resume normal capacity con-
trol operation after the override termination condition has
been satisfied. (In the case of high discharge superheat,
there is an intermediate stage.)
Table 14 summarizes these override parameters.
Other types of override events do not override control guide
vane or VFD operation, but are reported:
• High compressor discharge temperature override — If the
COMP DISCHARGE TEMP is greater than the COMP
DISCHARGE ALERT threshold, then high discharge tem-
perature override will be displayed in the main screen until
the COMP DISCHARGE TEMP is less than the COMP
DISCHARGE ALERT threshold – 2°F (1.1°C).
• High compressor bearing temperature override — If one of
the compressor bearing temperatures is greater than the
compressor bearing temperature Alert (Configuration

Menu Protective Limit Config) threshold, then High
Bearing Temp Override shall be active until all of the com-
pressor bearing temperatures are less than Comp Bearing
Temp Alert minus 2°F (1.1°C).
• Low Discharge Superheat Temperature Override — This
override is ignored during the first 5 minutes after chiller
start-up.
DEFAULT VALUE/
CONFIGURABLE
RANGE
55 psig/20 to 56 psig > COND PRESS OVER-
RIDE HIGH + 2.4 psi
200°F/125 to 200°F
(93.3°C/51.7 to 93.3°C)
104°F/90 to 120°F
(40°C/32.2 to 48.9°C)
< EVAP SAT OVERRIDE
TEMP - 1°F (0.56°C)
200°F/150 to 200°F COMP MOTOR WIND-
(93.3°C/65.6 to 93.3°C) ING TEMP > COMP
MOTOR TEMP OVER-
RIDE + 10°F (5.6°C)
PERCENT LINE CUR-
RENT > 105%; 102%
WHEN 32VS VFD
INSTALLED
< DSH REQUIRED –3
20
SECOND STAGE OVERRIDE
CAPACITY DECREASE TERMINATION
< COND PRESS
OVERRIDE HIGH —
1 psi
COMP DISCHARGE
TEMP
<COMP DISCHARGE
ALERT-2°F (1.1°C)
COMP BEARING
TEMP
<COMP BEARING
TEMP ALERT DV-2°F
(1.1°C)
> EVAP SAT OVER-
RIDE TEMP + 2°F
(1.1°C)
COMP MOTOR WIND-
ING TEMP < COMP
MOTOR TEMP OVER-
RIDE – 2°F (1.1°C)
>102% <98%
PERCENT LINE CUR-
RENT <= 100%
> DSH REQUIRED + 2
>LWT PROTECTION
SETPOINT + 0.5°F
(0.3°C)