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JOHNSON CONTROLS

SECTION 1 – DESCRIPTION OF SYSTEM AND FUNDAMENTALS OF OPERATION

FORM 160.69-O2

ISSUE DATE: 9/30/2020

brought on line. After this period has elapsed, the lag

compressor can be brought on line per normal opera-

tion. While this period is in effect, the lead compressor

motor current will be limited to the value programmed

for the

Lead Compressor Pulldown Demand Limit

Setpoint (30-100% FLA). This current limit applies to

the full load amps of the Lead compressor motor only,

not the Chiller Full Load Amps (total of both compres-

sors). For example, if the Chiller Full Load Amps is

2000A, then each compressor’s FLA is 1000A. If set

to 80%, then the lead compressor motor current would

be limited to 800A (80% x 1000) for the duration of

this period.
The CHILLER PULLDOWN DEMAND LIMIT

Setpoint (that was used during the CHILLER PULL-

DOWN PERIOD in previous software versions) has

been removed in this and later software versions. Al-

though this setpoint has been removed, the logic in

the CHILLER PULLDOWN PERIOD that is used to

determine if it is necessary to bring on the Lag com-

pressor (to meet load) still exists. This period is still

in effect from start until the Leaving Chilled Liquid

Temperature is within 2ºF of the Leaving Chilled Liq-

uid Temperature Setpoint. However, the “Chiller Pull-

down In Effect” LED (that indicated when the Chiller

Pulldown Period is in effect) has been eliminated from

the MOTOR Screen to avoid confusion with the Lead

Compressor Pulldown Demand Limit feature.
After the Lead Compressor Pulldown Time Setpoint

has elapsed, the chiller current limit will be limited to

the value programmed for the Chiller Current Limit

Setpoint. As in previous software versions, this setpoint

is applied to the total chiller current (30% to 100% of

the Chiller Full Load Amps). For example, if the Chill-

er FLA is 1600 Amps, the FLA of each motor is 800

Amps. If this setpoint is set to 70%, the Chiller Cur-

rent would be limited to 1120 Amps. If both compres-

sors are running, each would be limited to 560 amps. If

only one motor is running, the motor would be allowed

to operate all the way up to its full load amps of 800

Amps, because the total chiller current is being limited

to 1120 Amps.

Compressor Lockout

The COMPRESSOR LOCKOUT Setpoint, available

on the Capacity Compressor Cycling Screen, can be

used to lockout either compressor. The designated

compressor will not be permitted to run. This feature is

useful when it is desired to perform service on a com-

pressor.

With Software version C.OPT.11.03.01.004 (or later),

a single compressor can be locked out while both com-

pressors are running, without shutting down the entire

chiller. A soft shutdown will be performed on the run-

ning compressor selected for lockout and its status is

changed to “Lag” (if it is not the lag compressor al-

ready). Upon completion of Coastdown, the compres-

sor will remained locked out until the lockout is re-

leased. If there is only one compressor running and it is

the one targeted for lockout, the user will have to either

shutdown the entire chiller and then lockout the desired

compressor or bring the other compressor on line and

then lockout the desired one. In previous software ver-

sions, a compressor can only be locked out only while

it is shutdown.
With Software version C.OPT.11.03.01.004 (or lat-

er), the following Safety or Cycling Conditions on a

Locked-out compressor will not cause the other com-

pressor to shutdown. In previous software versions,

these cycling and safety conditions that occur on a

Locked Out compressor cause the other compressor to

shutdown or prevent it from starting.
“Motor Controller [#1/#2] – Contacts Open”
“Oil Pump [#1/#2] – Drive Contacts Open”
“Proximity Probe – Low Supply Voltage”
“Discharge [#1/#2] – Low Temperature”
“Discharge [#1/#2] – High Temperature”
“Oil Pump [#1/#2] - Differential Pressure Calibration”
“Oil Pump [#1/#2] – Pressure Transducer Out of

Range”
“Thrust Bearing [#1/#2] – Proximity Probe Clearance”
“Thrust Bearing [#1/#2] - Proximity Probe Out of

Range”
When any of these conditions occur on a locked out

compressor, they are displayed as Warnings. This al-

lows the user to know that a condition exists on the

locked compressor. The condition must be corrected

prior to the lock-out being removed from the compres-

sor. If it is not, the warning condition will revert back

to a safety as soon as the lockout is removed and will

cause the chiller to trip.