Evaporator Heater Control; Alarms; Chiller Run Contact; Flow Switch Control - York YVAA Installation, Operation & Maintenance Instructions Manual

FORM 201.28-NM1.1
ISSUE DATE: 1/31/2018

Evaporator Heater Control

The evaporator heater is controlled by ambient
air temperature. If no systems are running and the
ambient temperature drops below 4.4 °C (40°F), the
heater is turned ON. If no systems are running and
the temperature rises above 7.2°C (45°F) the heater is
turned OFF. Whenever a system is running, the evap-
orator heater is turned OFF. Both evaporator heater
outputs will always be turned ON and OFF together.
An under voltage condition will keep the heater OFF
until full voltage is restored to the system.
Compressor Heater Control
Each compressor has its own heater. The purpose of
the heater is to assure refrigerant does not condense
in the compressor. There is no oil sump, but refriger-
ant could possibly condense in the rotors or the motor
housing. The heater will be OFF whenever the respec-
tive compressor is running. As soon as the compressor
shuts OFF, the heater will turn ON as long as all motor
temperature sensors in the compressor read less than
70°C (158°F). The heater will turn OFF, if any internal
compressor motor temperature sensor reads more than
71.1°C (160°F).

Alarms

Each system has its own alarm. The Alarm output is ON
(dry contact closed) when no fault condition is pres-
ent and OFF (dry contact open) to indicate an alarm
situation. The Alarm will be activated (contacts open),
if any of the following are true.
• A System is faulted or inhibited from starting for
more than 5 seconds.
• The Unit is faulted or inhibited from starting for
more than 5 seconds.
• A System is locked out.
• The Unit is locked out.
• Power is removed from the chiller.

Chiller Run Contact

The Chiller Run dry contact is closed whenever any sys-
tem is running. It is open when all systems are shut OFF.

Flow Switch Control

A chilled liquid flow switch of suitable type MUST
be connected between Terminals 2 and 13 of 1TB to
provide protection against loss of liquid flow, which
will cause evaporator freeze-up if the chiller is
permitted to run.
JOHNSON CONTROLS

Remote Run / Stop

A Remote Run/Stop input is available for each system.

BASIC OPERATING SEQUENCE

Start Sequence and Loading

To initiate the start sequence of the chiller, the
following conditions must be satisfied before the pre-
charge of the DC Bus will take place:
• UNIT SWITCH must be ON.
• At least one System Switch is ON.
• Run permissive inputs (Remote Cycling Con-
tacts) must be closed.
• No unit faults exist.
• No unit start inhibits exist.
• At least one system not faulted or inhibited.
• The Daily Schedule is calling for the chiller to
run.
• The Flow Switch is closed.
• Leaving Chilled Liquid Setpoint is above the
Setpoint plus CR (Setpoint High Limit).
Once the precharge takes place, if the anti-recycle tim-
er is timed out the chiller control system on the Chiller
Control Board will select the number of compres-
sors to start and begin operation of the compressors.
The compressor(s) speed will be ramped to the mini-
mum start frequency and increase speed as needed in
an effort to regulate the leaving chilled liquid tempera-
ture to meet the desired Setpoint. Unit Warnings

UNIT WARNING

Unit Warning Operation

Unit warnings are caused when a condition is
present requiring operator intervention to restart the
unit. All setpoints, program values, and options should
be checked before operating the unit. Warnings are
not logged to the history buffer. If a unit warning is in
effect, the message will be displayed to the operator
when the STATUS key is pressed.

Low Battery Warning

The LOW BATTERY WARNING can only occur at
unit power-up. On micropanel power-up, the RTC
battery is checked to see if it is still operational. If
it is, normal unit operation is allowed. If the battery
voltage is determined to be low, the following warning
message is displayed indefinitely.
SECTION 7 - OPERATION
103
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