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Table 43 Thermistor Temperatures vs

Resistance, Motor Temperature Thermistors

Table 44 — Thermistor

(Liquid Level Sensor) Depth

Table 45 — Calibrating Pressure Transducers

(Pressure Gage Installed)

Safety Devices —

The 30GX/HX chillers contain many

safety devices and protection logic built into the electronic
control. Following is a description of the major safeties.

COMPRESSOR PROTECTION
Motor Overload — The compressor protection modules
(CPM) protect each compressor against overcurrent. Do not
bypass the current transducers or make any changes to the
factory-installed and configured 8 pin headers. The configura-
tion of these headers defines the Must Trip Amps (MTA) at
which the CPM will turn the compressors off. Determine the
cause for trouble and correct the problem before resetting the
CPM. See Appendix A for setting of MTAs and configuration
headers.

Each CPM board also reads the status of each compressor’s

high-pressure switch. All compressors have factory-installed
high-pressure switches. For 30GX units, the switch is set to trip
at 303

7 psig (2089

48 kPa). The setting for 30HXA units is

275

7 psig (1896

48 kPa) and for 30HXC units the setting

is 191

7 psig (1317

48 kPa). If the switch opens during op-

eration, the compressor will be shut down. The CPM will reset
automatically when the switch closes, however, a manual reset
is required to restart the compressor.
OIL SEPARATOR HEATERS (30GX) — Each oil separator
circuit has a heater mounted on the underside of the vessel.
The heater is energized with control circuit power. Oil heaters
are energized when the discharge gas temperature falls below
105 F (40.6 C). The heaters are deenergized when the dis-
charge gas temperature rises above 110 F (43.3 C). The control
will allow the chiller to attempt to start with the heaters ener-
gized and will keep the heaters on, even when running, until
the discharge gas temperature reaches 110 F (43.3 C). Note
that the oil heaters are deenergized if the oil level switch is
open.
COOLER PROTECTION
Low Water Temperature — Microprocessor is programmed
to shut the chiller down if the 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. When the fluid temperature rises 6

(3.3

C) above the leaving fluid set point, the safety resets and

the chiller restarts. Reset is automatic as long as this is the first
occurrence of the day.

Relief Devices —

Fusible plugs are located in each cir-

cuit (30GX only) between the condenser and the liquid line
shutoff valve.
PRESSURE RELIEF VALVES — Valves are installed in each
circuit and are located on all coolers. One relief valve is also
installed on each 30HXC condenser. Both circuits’ oil separa-
tors on 30GX and 30HXA units have factory-installed relief
valves as well. These valves are designed to relieve if an
abnormal pressure condition arises. Relief valves on all coolers
and 30HXC condensers relieve at 220 psi (1517 kPa). Relief
valves on 30GX and 30HXA oil separators relieve at 320 psi
(2206 kPa). All 30HXA, HXC units with factory-installed suc-
tion service valves also have a relief valve in each compressor
discharge line. These valves are designed to relieve at 350 psig
(2413 kPa). These valves should not be capped. If a valve
relieves, it should be replaced. If the valve is not replaced, it
may relieve at a lower pressure, or leak due to trapped dirt
from the system which may prevent resealing.

Pressure relief valves located on cooler and condenser shells

and 30HXA oil separator shells have

-in. NPT connections

for relief. The 30GX oil separators have

-in. male flare con-

nections. Some local building codes require that relieved gases
be removed. This connection allows conformance to this
requirement.

TEMP

(F)

TEMP

(C)

RESISTANCE

(Ohms)