Carrier AquaEdge 19XR, Controls Operation And Troubleshooting

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DEMAND LIMIT SOURCE exceeds the ACTIVE DEMAND

LIMIT by 5% or less, capacity will be inhibited. If the DE-

MAND LIMIT SOURCE exceeds the ACTIVE DEMAND

LIMIT by more than 5%, capacity will be decreased.

Alternatively, the limit may be applied by AUTO DE-

MAND LIMIT INPUT, an optional 4 to 20 mA input. This de-

mand limit control option (4 to 20 mA DEMAND LIMIT

TYPE) is externally controlled by a 4 to 20 mA signal. The op-

tion is set up on the Configuration Menu 



 GENERAL CON-

FIGURATION screen. When enabled, 4 mA will set ACTIVE

DEMAND LIMIT to 100% of the DEMAND LIMIT

SOURCE (regardless of the value of BASE DEMAND LIM-

IT), and 20 mA will set ACTIVE DEMAND LIMIT to the val-

ue configured for DEMAND LIMIT AT 20 mA in the Config-

uration Menu 



 SERVICE PARAMETERS screen. 

OVERRIDE CONTROL — Capacity overrides can prevent

some safety shutdowns caused by exceeding the motor am-

perage 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 ca-

pacity control:

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 PIC 5 con-

troller indicates the reason for the override. Normal ca-

pacity control operation is restored when the value cross-

es 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 PIC 5 controls resume normal capacity

control operation after the override termination condition

has been satisfied. (In the case of high discharge super-

heat, there is an intermediate stage.)

Table 15 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 — For

compressor/frame 6 and 7, 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 DIS-

CHARGE TEMP is less than the COMP DISCHARGE

ALERT threshold – 2° F (1.1° C).

• High compressor bearing temperature override — For

compressor/frame 6 and 7, if one of the compressor bear-

ing temperatures is greater than the compressor bearing

temperature Alert (Configuration Menu 



 Protective

Limit Config) threshold, then High Bearing Temp Over-

ride shall be active until all of the compressor bearing

temperatures are less than Comp Bearing Temp Alert

minus 2° F (1.1° C). For compressors 2-6, D, and E, if

the calculated compressor bearing temperature is greater

than the bearing temperature alert threshold, then high

bearing temperature override will be active until the cal-

culated bearing temperature is less than the threshold

minus 2° F (1.1° C). 

• Low Discharge Superheat Temperature Override — This

override is ignored during the first 5 minutes after chiller

start-up. There are additional requirements for normal

override function after start-up. For compressor E, con-

denser pressure must be 10 psi greater than cooler pres-

sure; for compressor/frame 6 and 7, the damper must

have been open for 20 consecutive seconds.

RECYCLE CONTROL — The  chiller  may  cycle  off  and

wait until the load increases to restart when the compressor

is running in a lightly loaded condition. This normal cycling

is known as “recycle.” 

In cooling mode, a recycle shutdown is initiated when either

of the following conditions is true: 
• Leaving chilled water temperature (or entering chilled

water temperature, if the EWT CONTROL OPTION is

enabled) is more than 5° F (2.8° C) below the CON-

TROL POINT. 

• Leaving chilled water temperature (or entering chilled

water temperature, if the EWT CONTROL OPTION is

enabled) is below the CONTROL POINT, and the chilled

water temperature difference is less than the RECYCLE

SHUTDOWN DELTA T.
In heating mode, a recycle cycle shutdown occurs when ei-

ther of the following conditions is true:
• Leaving condenser water temperature (or entering con-

denser water temperature, if the EWT CONTROL

OPTION is enabled) is more than 5° F (2.8° C) below the

CONTROL POINT. 

• Leaving condenser water temperature (or entering con-

denser water temperature, if the EWT CONTROL

OPTION is enabled) is above the CONTROL POINT,

and the condenser water temperature difference is less

than the RECYCLE SHUTDOWN DELTA T.

NOTE: Recycle shutdown will not occur if the CONTROL

POINT has been changed by more than 1° F (0.56° C) within

the previous 5 minutes of operation. 

When the chiller is in RECYCLE mode, the chilled water

pump relay remains energized so the chilled water temperature

can be monitored for increasing load. The recycle control uses

RECYCLE RESTART DELTA T to check when the compres-

sor should be restarted. In cooling mode, the compressor will

restart when the leaving chilled water temperature (or entering

chilled water temperature, if the EWT CONTROL OPTION is

enabled) is greater than the CONTROL POINT plus the RE-

CYCLE RESTART DELTA T for 5 consecutive seconds. In

heating mode, the compressor will restart when the leaving

condenser water temperature (or entering condenser water tem-

perature, if the EWT CONTROL OPTION is enabled) is less

than the CONTROL POINT minus the RECYCLE RESTART

DELTA T for 5 consecutive seconds.
RUNNING TIMERS AND COUNTERS — The PIC 5 con-

trol maintains two run-time clocks: COMPRESSOR ONTIME

and SERVICE ONTIME. COMPRESSOR ONTIME indicates

the total lifetime compressor run hours. SERVICE ONTIME is

a resettable timer that can be used to indicate the hours since

the last service visit or any other event. A separate counter tal-

lies compressor starts as TOTAL COMPRESSOR STARTS.

All of these can be viewed on the RUN TIMES screen. Both

Ontime counters roll over to 0 at 500,000 hours. Manual

changes to SERVICE ONTIME from the screen are permitted

at any time. If the controller is replaced, one opportunity before

the first start-up with the new controller is provided to set

COMPRESSOR ONTIME and TOTAL COMPRESSOR

STARTS to the last readings retained with the prior controller. 

The chiller also maintains a start-to-start timer and a stop-

to-start timer. These timers limit how soon the chiller can be

started and are displayed on the system overview (home) and

RUN TIMES screens. They can be configured in the Config-

uration Menu 



 GENERAL CONFIGURATION screen.

They must expire before the chiller starts. If the timers have

not expired, the RUN STATUS parameter on the System

Overview (Home) and GENERAL PARAMETERS screen

reads TIMEOUT.