Basic Operating Sequence - York YVAA Installation Operation & Maintenance

Form 201.47-ICOM1
Issue date: 17/11/2022
Both evaporator heater outputs are always turned ON
and OFF together. An under voltage condition keeps
the heater OFF until full voltage is restored to the sys-
tem.
Chiller controller cannot detect the failure
of all the heaters used in compressor, oil
separator, evaporator shell and evaporator
water box, etc. with the chilled water pump
running and with the evaporator heaters
well maintained are extremely crucial
especially in subfreezing regions. Chilled
water pump control contains the logic for
prevention of evaporator freezing.
Compressor heater control
Each compressor has its own heater. The purpose of
the heater is to ensure 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.
JOHNSON CONTROLS
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.
Changing the switch point of the thermal
dispersion flow switch
To change the factory-set LED 7, complete the follow-
ing steps:
1. Press the ◄ or ► push button. The switch point
LED flashes.
2. Press the ◄ or ► push button as many times
as required in less than 2 seconds between each
press. Each press of the push button shifts the
LED by one position in the indicated direction.
3. Stop pressing the button when the switch posi-
tion LED changes to the required position. The
flow switch automatically returns to the operating
mode with the new setting in 2 seconds.
4. To prevent unintentional settings, press both push
buttons simultaneously for at least 10 seconds in
operating mode to lock the switch electronical-
ly. To unlock the flow switch, perform the same
operation again. The setting remains the same in
case of power failure.
Run permissive
A Run permissive 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.
SECTION 7 - OPERATION
101
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