21
Chiller Dehydration
Dehydration is recommended if the chiller has been open for a
considerable period of time, if the chiller is known to contain
moisture, or if there has been a complete loss of chiller holding
charge or refrigerant pressure.
Dehydration can be done at room temperatures. Using a cold
trap (Fig. 18) may substantially reduce the time required to com-
plete the dehydration and is recommended should the unit be ex-
posed to liquid moisture. The higher the room temperature, the
faster dehydration takes place. At low room temperatures, a very
deep vacuum is required to boil off any moisture and heating of
the water in the water circuits of the chiller to approximately
100°F (38°C) may be required.
Fig. 18 — Dehydration Cold Trap
Perform dehydration as follows:
1. Connect a high capacity vacuum pump (5 cfm [.002 m
3
/s]
or larger is recommended) to the refrigerant vacuum/
charging valve (Fig. 2). Tubing from the pump to the
chiller should be as short in length with a minimum diam-
eter of 0.5 in. (13 mm) and as large in diameter as possible
to provide least resistance to gas flow.
2. Use an absolute pressure manometer or a electronic
micron gage to measure the vacuum. Open the shutoff
valve to the vacuum indicator only when taking a reading.
Leave the valve open for 3 minutes to allow the indicator
vacuum to equalize with the chiller vacuum.
3. If the entire chiller is to be dehydrated, open all isolation
valves (if present).
4. With the chiller ambient temperature at 60°F (15.6°C) or
higher, operate the vacuum pump until the manometer
reads 185 psig (1275 kPa), or a vacuum indicator reads
35°F (1.7°C). Operate the pump an additional 2 hours.
5. Do not apply a greater vacuum than 29.73 in. Hg vac
(755.1 mm Hg) or go below 33°F (0.56°C) on the wet bulb
vacuum indicator. At this temperature and pressure, isolated
pockets of moisture can turn into ice. The slow rate of evap-
oration (sublimation) of ice at these low temperatures and
pressures greatly increases dehydration time.
6. Valve off the vacuum pump, stop the pump, and record the
instrument reading.
7. After a 2-hour wait, take another instrument reading. If the
reading has not changed, dehydration is complete. If the
reading indicates vacuum loss, repeat Steps 4 and 5.
8. If the reading continues to change after several attempts,
perform a leak test (maximum 160 psig [1103 kPa] pres-
sure). Locate and repair the leak, and repeat dehydration.
9. Once dehydration is complete, the evacuation process can
continue. The final vacuum prior to charging the unit with
refrigerant should in all cases be 29.9 in. Hg (500 microns,
0.07 kPa [abs]) or less.
Inspect Water Piping
Refer to piping diagrams provided in the certified drawings and
the piping instructions in the 19MV Installation Instructions man-
ual. Inspect the piping to the evaporator and condenser. Be sure
that the flow directions are correct and that all piping specifica-
tions have been met.
Piping systems must be properly vented with no stress on water-
box nozzles and covers. Water flows through the evaporator and
condenser must meet job requirements. Measure the pressure drop
across the evaporator and the condenser.
Check Safety Valves
Be sure safety valves have been piped to the outdoors in compli-
ance with the latest edition of ANSI/ASHRAE Standard 15 and
applicable local safety codes. Piping connections must allow for
access to the valve mechanism for periodic inspection and leak
testing.
The standard 19MV relief devices are set to relieve at 185 psig
(1275 kPa) chiller design pressure.
Ground Fault Troubleshooting
Follow this procedure only if ground faults are declared by the
chiller controls. Test the chiller compressor motor and its power
lead insulation resistance with a 500-v insulation tester such as a
megohmmeter.
1. Open the VFD main disconnect switch and follow lockout/
tagout rules.
2. Perform test 1: For 3-lead motor, tie terminals 1, 2, and 3
together and test between the group and ground.
a. With the tester connected to the motor leads, take 10-sec-
ond and 60-second megohm readings.
b. Divide the 60-second resistance reading by the 10-
second reading. The ratio, or polarization index, must
be one or higher. Both the 10 and 60-second readings
must be at least 50 megohms. If the readings are
unsatisfactory, repeat the test at the motor with the
power leads disconnected. Satisfactory readings in
this second test indicate the fault is in the power leads.
3. Perform test 2: Only perform this test if the unit has been
disassembled at the job site, if the starter has been
removed, or during annual maintenance.
Perform a megohm test from each terminal to ground. The
megohm value should be greater than 20 megohm. Note that
if a megohm test is performed between the terminals it will
show a direct short and is not a valid test because of the 3 ter-
minal motor internal delta configuration.
CAUTION
Do not start or megohm-test the compressor motor or any
other pump motor, even for a rotation check, if the chiller is
under dehydration vacuum. Insulation breakdown and severe
damage may result.
WARNING
Power to the motor and VFD must be disconnected by an iso-
lation switch before placing the machine under a vacuum. To
be safe, isolate input power before evacuating the chiller if you
are not sure if there are live leads to the hermetic motor.
CAUTION
Water must be within design limits, clean, and treated to en-
sure proper chiller performance and to reduce the potential of
tube damage due to corrosion, scaling, or erosion. Carrier as-
sumes no responsibility for chiller damage resulting from un-
treated or improperly treated water.
CAUTION
The motor leads must be disconnected from the VFD before
an insulation test is performed. The voltage generated from the
tester can damage the VFD.
Содержание AquaEdge 19MV
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