Indication Of Low Charge On A 30Hxc System; Electrical Maintenance; Pressure Transducers; Oil Charging - Low Oil Recharging - Carrier 30HXC Installation, Operation And Maintenance Instructions

12.4 - Indication of low charge on a 30HXC system

NOTE : To check for low refrigerant charge on a 30HXC, several
factors must be considered. A flashing liquid-line sightglass is
not necessarily an indication of inadequate charge. There are
many system conditions where a flashing sightglass occurs under
normal operation. The 30HXC metering device is designed to
work properly under these conditions.
1. Make sure that the circuit is running at a full-load condition.
To check whether circuit A is fully loaded, follow the procedure
described in the Controls manual.
2. It may be necessary to use the Manual Control feature to
force the circuit into a full-load condition. If this is the case,
see the instructions for using the Manual Control feature in
the Controls manual.
3. With the circuit running at full-load, verify that the cooler
leaving fluid temperature is in the range of 6°C ± 1.5 K.
4. At this condition, observe the refrigerant in the liquid line
sightglass. If there is a clear sightglass, and no signs of flashing,
then the circuit is adequately charged. Skip the remaining
steps.
5. If the refrigerant appears to be flashing, the circuit is probably
low on charge. Verify this by checking the EXV position (see
30GX/HXC Pro-Dialog Plus Controls IOM).
6. If the opening position of the EXV is greater than 60%, and
if the liquid-line sightglass is flashing, then the circuit is low
on charge. Follow the procedure for adding charge.
12.4.1 - To add charge to the 30HXC systems
1. Make sure that the unit is running at full-load, and that the
cooler leaving fluid temperature is in the range of 5.6 to
7.8°C.
2. At these operating conditions, check the liquid-line sightglass.
If there is a clear sightglass, then the unit has sufficient
charge. If the sightglass is flashing, then check the EXV
Percent Open. If this is greater than 60%, then begin adding
charge.
NOTE: A flashing liquid-line sightglass at operating conditions
other than those mentioned above is not necessarily an indication
of low refrigerant charge.
3. Add 2.5 kg of liquid charge into the evaporator using the
charging valve located on the top of the evaporator.
4. Observe the EXV Percent Open value. The EXV should
begin closing as charge is being added. Allow the unit to
stabilize. If the EXV Percent Open remains above 60%, and
there are still bubbles in the sightglass, add an additional 2.5
kg of liquid charge.
5. Allow the unit to stabilize, and again check the EXV Percent
Open. Continue adding 2.5 kg of liquid refrigerant charge
at a time, and allow the unit to stabilize before checking the
EXV position.
6. When the EXV Percent Open is in the range of 40-60%, check
the liquid line sightglass. Slowly add enough additional liquid
charge to ensure a clear sightglass. This should be done
slowly to avoid overcharging the unit.
7. Verify adequate charge by continuing to run at full-load with
6°C ± 1.5 K evaporator leaving fluid temperature. Check
that the refrigerant is not flashing in the liquid-line sightglass.
The EXV Percent Open should be between 40 and 60%. The
cooler level indicator should be in the range of 1.5 - 2.5.

12.5 - Electrical maintenance

When working on the unit comply with all safety precautions
decribed in section "Maintenance safety considerations".
It is strongly recommended to change the fuses in the units
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every 15000 operating hours or every 3 years.
It is recommended to verify that all electrical connections
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are tight:
- after the unit has been received at the moment of
installation and before the first start-up,
-
one month after the first start-up,when the electrical
components have reached their nominal operating
temperatures,
- then regularly once a year.

12.6 - Pressure transducers

12.6.1 - Discharge pressure (circuits A and B)
This input is used to measure the high side pressure of each circuit
of the unit. It is used to provide the pressure to replace the
discharge pressure gauge and to control the head pressure.
12.6.2 - Suction pressure (circuits A and B)
This input is used to measure the pressure of the low side of the
unit. It is used to provide the pressure to replace the suction
pressure gauge.
12.6.3 - Oil pressure (each compressor)
This input is used to measure the oil pressure of each unit
compressor. It is located on the oil pressure port of each
compressor.
12.6.4 - Economizer pressure (circuits A and B)
This input is used to monitor the oil pressure differential supplied
to the compressor.

12.7 - Oil charging - low oil recharging

12.7.1 - Addition of oil charge to 30HXC systems
1. If the 30HXC unit shuts-off repeatedly on Low oil Level, this
may be an indication of inadequate oil charge. It could also
mean simply that oil is in the process of being reclaimed
from the low-side of the system.
2. Begin by running the unit at full-load for an hour and a half.
3. After running for 1-1/2 hours allow the unit to re-start and run
normally. If the Low Oil Level alarms persist, the unit has a low
oil charge. Add oil to the oil separator, using the oil charging
valve at the bottom of the condenser.
CAUTION: Do NOT add oil at any other location as improper
unit operation may result.
4. Make sure that the unit is not running when adding oil, as
this will make the oil charging process easier. Because the
system is under pressure even when the unit is not running,
it will be necessary to use a suitable pump (hand or electric
pump) to add oil to the system.
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