Safety Devices; Compressor Protection; Low Oil Pressure Protection; Cooler Protection - Carrier Air Conditioner Operation And Service Manual

Air-cooled reciprocating liquid chillers with comfortlink controls 50/60 hz
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Safety Devices —
Chillers contain many safety devices
and protection logic built into electronic control. Following is a
brief summary of major safeties.

COMPRESSOR PROTECTION

Circuit Breaker — One manual-reset, calibrated-trip magnetic
circuit breaker for each compressor protects against overcur-
rent. Do not bypass or increase size of a breaker to correct
problems. Determine cause for trouble and correct before
resetting breaker. Circuit breaker must-trip amps (MTA) are
listed on individual circuit breakers, and on unit label
diagrams.
30GTN,R and 30GUN,R070 (50 Hz), 080-110 and 230B-
315B Compressor Protection Board (CPCS) — The CPCS is
used to control and protect compressors and crankcase heaters.
Board provides following features:
• compressor contactor control
• crankcase heater control
• ground current protection
• status communication to processor board
• high-pressure protection
One large relay is located on CPCS that controls crankcase
heater and compressor contactor. In addition, this relay pro-
vides a set of contacts that the microprocessor monitors to de-
termine operating status of compressor. If the MBB determines
that compressor is not operating properly through signal con-
tacts, control locks compressor off.
The CPCS contains logic that can detect if current-to-
ground of any winding exceeds 2.5 amps; if so, compressor
shuts down.
A high-pressure switch with a trip pressure of 426 ± 7 psig
(2936 ± 48 kPa) is mounted on each compressor; switch setting
is shown in Table 34. Switch is wired in series with the CPCS.
If switch opens, CPCS relay opens, processor detects it through
signal contacts, and compressor locks off. A loss-of-charge
switch is also wired in series with the high-pressure switch and
CPCS.
If any of these switches opens during operation, the com-
pressor stops and the failure is detected by the MBB when sig-
nal contacts open. If lead compressor in either circuit is shut
down by high-pressure switch, ground current protector, loss of
charge switch, or oil pressure switch, all compressors in the cir-
cuit are locked off.
30GTN,R and 30GUN,R 130-210, 230A-315A and
330A/B-420A/B — A control relay in conjunction with a
ground fault module replaces the function of the CPCS
(above). To reset, press the push-button switch (near the Mar-
quee display).
Table 34 — Pressure Switch Settings,
psig (kPa)
SWITCH
CUTOUT
CUT-IN
High Pressure
426 ± 7
320 ± 20
30GTN,R Units
(2936 ± 48)
(2205 ± 138)
High Pressure
280 ± 10
180 ± 20
30GUN,R Units
(1830 ± 69)
(1240 ± 138)
Loss-of-Charge
7 (48.2)
22 (151.6)
LOW OIL PRESSURE PROTECTION — Lead
compres-
sor in each circuit is equipped with a switch to detect low oil
pressure. Switch is connected directly to processor board.
Switch is set to open at approximately 5 psig (35 kPa) and to
close at 9 psig (62 kPa) maximum. If switch opens when
compressor is running, CR or processor board stops all com-
pressors in circuit. During start-up, switch is bypassed for
2 minutes.
CRANKCASE HEATERS — Each compressor has a 180-w
crankcase heater to prevent absorption of liquid refrigerant by
oil in crankcase when compressor is not running. Heater power
source is auxiliary control power, independent of main unit
power. This assures compressor protection even when main
unit power disconnect switch is off.
IMPORTANT: Never open any switch or disconnect
that deenergizes crankcase heaters unless unit is being
serviced or is to be shut down for a prolonged period.
After a prolonged shutdown or service, energize crank-
case heaters for 24 hours before starting unit.

COOLER PROTECTION

Freeze Protection — Cooler can be wrapped with heater
cables as shown in Fig. 34, which are wired through an ambi-
ent temperature switch set at 36 F (2 C). Entire cooler is cov-
ered with closed-cell insulation applied over heater cables.
Heaters plus insulation protect cooler against low ambient tem-
perature freeze-up to 0° F (–18 C).
IMPORTANT: If unit is installed in an area where ambi-
ent temperatures fall below 32 F (0° C), it is recom-
mended that inhibited ethylene glycol or other suitable
corrosion-inhibitive antifreeze solution be used in
chilled-liquid circuit.
Low Fluid Temperature — Main Base Board is programmed
to shut chiller down if leaving fluid temperature drops below
34 F (1.1 C) for water or more than 8° F (4.4° C) below set
point for brine units. The unit will shut down without a
pumpout. When fluid temperature rises to 6° F (3.3° C) above
leaving fluid set point, safety resets and chiller restarts. Reset is
automatic as long as this is the first occurrence.
Loss of Fluid Flow Protection — Main Base Board contains
internal logic that protects cooler against loss of cooler flow.
Entering and leaving fluid temperature sensors in cooler detect
a no-flow condition. Leaving sensor is located in leaving fluid
nozzle and entering sensor is located in first cooler baffle space
in close proximity to cooler tubes, as shown in Fig. 34. When
there is no cooler flow and the compressors start, leaving fluid
temperature does not change. However, entering fluid temper-
ature drops rapidly as refrigerant enters cooler through EXV.
Entering sensor detects this temperature drop and when enter-
ing temperature is 3° F (1.6° C) below leaving temperature,
unit stops and is locked off.
Loss-of-Charge — A pressure switch connected to high side
of each refrigerant circuit protects against total loss-of-charge.
Switch settings are listed in Table 34. If switch is open, unit
cannot start; if it opens during operation, unit locks out and
cannot restart until switch is closed. Low charge is also moni-
tored by the processor when an EXV is used. The loss-of-
charge switch is wired in series with the high-pressure switch
on each circuit’s lead compressor.
LEGEND
T — Thermistor
Fig. 34 — Cooler Heater Cables
Page 64

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