Daikin WDC Installation, Operation And Maintenance Manual page 64

Refrigerant Cycle
Maintenance of the refrigerant cycle includes maintaining a log
of the operating conditions, and checking that the unit has the
proper oil and refrigerant charge.
At every inspection, the oil, suction, and discharge pressures
should be noted and recorded, as well as condenser and chiller
water temperatures.
The suction line temperature at the compressor should
be taken at least once a month. Subtracting the saturated
temperature equivalent of the suction pressure from this will
give the suction superheat. Extreme changes in subcooling
and/or superheat over a period of time will indicate losses
of refrigerant or possible deterioration or malfunction of the
expansion valves. Proper superheat setting is 0 to 1 degree F
(0.5 degree C) at full load. Such a small temperature difference
can be difficult to measure accurately. Another method is to
measure the compressor discharge superheat, the difference
between the actual discharge temperature and the saturated
discharge temperature. The discharge superheat should be
between 14 and 16 degrees F (8 to 9 degrees C) at full load.
The liquid injection must be deactivated (by closing the valve
in the feed line) when taking the discharge temperature. The
superheat will increase linearly to 55 degrees F (30 degrees C)
at 10% load. The MicroTech II interface panel can display all
superheat and subcooling temperatures.
Electrical System
Maintenance of the electrical system involves the general
requirement of keeping contacts clean and connections tight
and checking on specific items as follows:
1. The compressor current draw should be checked
and compared to nameplate RLA value. Normally,
the actual current will be lower, since the nameplate
rating represents full load operation. Also check all
pump and fan motor amperages, and compare with
nameplate ratings.
2. Inspection must verify that the oil heaters are
operative. The heaters are insert-cartridge type and
can be checked by ammeter reading. They should be
energized whenever power is available to the control
circuit, when the oil temperature sensor calls for heat,
and when the compressor is inoperative. When the
compressor runs, the heaters are de-energized. The
Digital Output screen and second View screen on
the operator interface panel both indicate when the
heaters are energized.
3. At least once a quarter, all equipment protection
controls except compressor overloads should be
made to operate and their operating points checked.
A control can shift its operating point as it ages, and
this must be detected so the controls can be adjusted
or replaced. Pump interlocks and flow switches should
be checked to be sure they interrupt the control circuit
when tripped.
4. The contactors in the motor starter should be
inspected and cleaned quarterly. Tighten all terminal
IOM 1281-2 • CENTRIFUGAL WATER CHILLERS
connections.
5. The compressor motor resistance to ground should be
checked and logged semi-annually. This log will track
insulation deterioration. A reading of 50 megohms or
less indicates a possible insulation defect or moisture
and must be further checked.
6. The centrifugal compressor must rotate in the
direction indicated by the arrow on the rear motor
cover plate, near the rotation sight glass. If the
operator has any reason to suspect that the power
system connections have been altered (phases
reversed), the compressor must be jogged clockwise
to check rotation. For assistance, call the local Daikin
Applied service location.
Never Megger a motor while in a vacuum. Severe motor
damage can result.
Cleaning and Preserving
A common cause of service calls and equipment malfunction
is dirt. This can be prevented with normal maintenance. The
frequency of service will vary with each installation.
1. Remove and clean strainers in chilled water system,
oil cooler line and condenser water system at every
inspection.
2. Inspect the condenser tubes annually for fouling and
clean if required. The dished water heads (aka end-bells,
water boxes) should be removed with care due to their
weight. One method follows:
• After draining water, remove all but four head bolts at
roughly 10 and 2 o'clock and 4 and 8 o'clock.
• Loosen the remaining four bolts to enable the head to be
separated from the tube sheet sufficiently for a clevis pin
or hook to be inserted into an open bolt hole at the top of
the head.
• Attach a hoist to the pin or hook, lift the head to remove
weight from the remaining bolts, remove the bolts and
carefully remove the head.
• Do not try to install an eyebolt with machine threads into
the head vent fitting, which has pipe threads.
• Reverse this procedure to mount the head, using a new
gasket.
Annual Shutdown
Seasonal Servicing
Prior to shutdown periods and before starting up again, the
following service procedures must be completed.
Where the chiller can be subject to freezing temperatures,
the condenser and chiller must be drained of all water. Dry
air blown through the condenser will aid in forcing all water
out. Removal of condenser heads is also recommended. The
condenser and evaporator are not self-draining and tubes
must be blown out. Water permitted to remain in the piping
64
Maintenance
CAUTION
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