Setpoint And Remote Offset; First Time Start Up; Interlocks; Unit Switch - York YVAA Installation, Operation & Maintenance Instructions Manual

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

Setpoint and Remote Offset

Set the required leaving chilled liquid temperature
setpoint and Control Range under the SETPOINTS key.
The chilled liquid temperature control settings need to
be set according to the required operating conditions.
If remote temperature reset (offset) is to be used, the
maximum reset required must be programmed by
pressing the SETPOINTS key (see "Setpoints Key" on
page 145).

FIRST TIME START UP

During the commissioning period there
should be sufficient heat load to run the
unit under stable full load operation to
enable the unit controls, and system op-
eration to be set up correctly, and a com-
missioning log taken.

Interlocks

Verify that liquid is flowing through the evaporator
and that heat load is present. Ensure that any remote
run interlocks are in the run position and that the Daily
Schedule requires the unit to run or is overridden.

Unit Switch

Place the UNIT switch on the keypad to the ON position.

Startup

Press the SYSTEM SWITCHES key and place the
system switch for System 1 to the ON position. There
may be a few seconds delay before the first compres-
sor starts because of the anti-recycle timer). Be ready
when each compressor starts, to switch the UNIT
switch OFF immediately, if any unusual noises or
other adverse conditions develop.
When a compressor is running, the controller monitors
oil pressure, motor current, and various other system
parameters such as discharge pressure, chilled liquid
temperature, and so on. Should any problems occur;
the control system will immediately take appropriate
action and display the nature of the fault.
JOHNSON CONTROLS

Oil Pressure

When a compressor starts, press the relevant "System
Pressures" key and verify that oil differential pressure
(oil pressure-suction pressure) develops immediately.
If oil pressure does not develop, the automatic con-
trols will shut down the compressor. Under no circum-
stances should a restart attempt be made on a compres-
sor, which does not develop oil pressure immediately.
Switch the UNIT switch to the OFF position.

Loading

Once the unit has been started, all operations are fully
automatic. After an initial period at minimum capacity,
the control system will adjust the unit load depending
on the chilled liquid temperature and rate of tempera-
ture change. If a high heat load is present, the control-
ler will increase the speed of the compressor(s).

Condenser and Fan Rotation

Once a compressor is running, discharge pressure
rises as refrigerant is pumped into the air-cooled con-
denser coils. This pressure is controlled by stages of
fans to ensure maximum unit efficiency while main-
taining sufficient pressure for correct operation of the
condensers and the lubrication system.
As discharge pressure rises, the condenser fans operate
in stages or ramp up in speed to control the pressure.
Verify that the fans operate in the correct direction of
rotation and operation is correct for the type of unit.

System Charge

Check system charge at steady full compressor load
only. It is important that all fans are running for the
system. The refrigerant level in the evaporator should
be about in the middle of the sight glass. Unless
levels are at the bottom or the top of the sight glass,
they should not cause concern or require adding or
removing charge.
SECTION 6 - COMMISSIONING
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