Override Control - Carrier PIC 5+ User Manual

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.
1. 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 PIC 5+ 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.
2. 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 PIC 5+ 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~E/V/D 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 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 closed for a consecutive 20 seconds; for 19DV, Ignore low discharge
superheat override during first 5 minutes after chiller startup completed.
Override Condition Override Parameter
High Condenser
CONDENSER
Pressure OVERRIDE
PRESSURE
(185Psi condenser)
High Condenser
CONDENSER
Pressure OVERRIDE
PRESSURE
(300Psi Condenser)
High Condenser
CONDENSER
Pressure OVERRIDE
PRESSURE
(44Psi condenser)
High Condenser
CONDENSER
Pressure OVERRIDE
PRESSURE
(72Psi Condenser)
CALC EVAP SAT TEMP
Low Evaporator or
Temperature override EVAP REFRIG LIQUID
TEMP
High Motor
COMP MOTOR
Temperature
WINDING TEMP
OVERRIDE
High CURRENT PERCENT LINE
override CURRENT
Low Discharge
Discharge Superheat
Superheat Override
Leaving chilled water
Low Source Temp
temperature (Heating
Protection Override
mode)
26
Configurable Range
First Stage Capacity Inhibit
Value
> COND PRESS OVERRIDE For low condenser type
LOW 140psig (90 - 157 psig)
> COND PRESS OVERRIDE For high condenser type
HIGH 250 psig (200 – 265 psig)
> COND PRESS OVERRIDE For low condenser
DV 44 type20psig (18 - 25psig)
> COND PRESS OVERRIDE For high condenser type
DV 72 55 psig (20 – 56 psig)
< EVAP SAT OVERRIDE
TEMP
Note: EVAP SAT OVERRIDE
TEMP = EVAP TRIPPOINT +
EVAP OVERRIDE DELTA T
> COMP MOTOR TEMP 200 F
OVERRIDE 150 to 200 F
PERCENT LINE CURRENT
> 100%
or RECTIFIER OVERLOAD
(Only for 32VS VFD) > 100%
< DSH REQUIRED + 1
Second Stage Capacity
Decrease
> COND PRESS OVERRIDE
HIGH + 2.4 psi
> COND PRESS OVERRIDE LOW
+ 2.4 psi
> COND PRESS OVERRIDE
HIGH + 2.4 psi
> COND PRESS OVERRIDE LOW
+ 2.4 psi
< EVAP SAT OVERRIDE TEMP – 1F
COMP MOTOR WINDING TEMP
> COMP MOTOR TEMP
OVERRIDE + 10 F (5.6 C)
PERCENT LINE CURRENT >
105%
(If 32VS VFD is installed,
PERCENT LINE CURRENT or
RECTIFIER OVERLOAD > 102%)
< DSH REQUIRED – 3
< LWT Protection Setpoint
(Protective Limit Config)– 2F
Override Termination
< COND PRESS
OVERRIDE HIGH - 1 psi
< COND PRESS
OVERRIDE LOW - 1 psi
< COND PRESS
OVERRIDE HIGH - 1 psi
< COND PRESS
OVERRIDE LOW - 1 psi
> EVAP SAT OVERRIDE
TEMP
COMPR MOTOR
WINDING TEMP < COMP
MOTOR TEMP OVERRIDE
- 2 F (1.1 C)
PERCENT LINE
CURRENT <= 100%
> DSH REQUIRED + 2
> LWT Protection Setpoint
(Protective Limit Config)– 2F