65
Pressure Transducers —
Discrete high and low pres-
sure transducers are used for pressure sensing on all
30GXN,GXR,HX chillers. The discharge and oil pressure
transducers are high pressure transducers, and the suction and
economizer pressure transducers are low pressure transducers
(white dot). No pressure transducer calibration is required. The
transducers operate on a 5 vdc supply, which is generated by
the Main Base Board (MBB) for suction and discharge
pressure transducers and by the Screw Compressor Board
(SCB) for the oil and economizer pressure transducers. See
unit wiring labels for specific MBB and SCB pressure
transducer power and signal connections. Refer to Fig. 35A-
35C for pressure transducer locations.
TROUBLESHOOTING — If transducer is suspected of being
faulty, first check supply voltage to transducer. Supply voltage
should be 5 vdc
±
.2 v. If supply voltage is correct, compare
pressure reading displayed on keypad and display module
against pressure shown on a calibrated pressure gage. If the
2 pressure readings are not reasonably close, replace pressure
transducer. Low pressure transducers suction and economizer
pressures should be within ± 2 psig. Discharge and oil
pressures should be within ± 5 psig.
FLOW SENSOR — Figure 36 shows a typical view of the
flow sensor as attached to a victaulic nozzle. It also shows the
connector pin orientation of the sensor. If nuisance trips of the
sensor are occurring, follow the steps below to correct the
situation:
When power is supplied to the device, a warm-up period is
initiated. During this period, the right-most green LED is lit
and turned off as each LED to the left is successively lit until
the left-most red LED is lit. The warm-up period may take up
to 30 seconds. When some flow is detected but not enough for
machine operation, a red LED at the far left will be illuminated.
With increasing flow, successive red LEDs illuminate. When
the switch determines flow is present, the amber LED illumi-
nates indicating the output has closed.
This is not an indica-
tion of minimum flow.
Increasing flow above the amber LED
output indication illuminates the first green LED. Each succes-
sive green LED indicates greater flow. The switch closure does
not indicate minimum flow for the machine. With one green
LED lit, minor fluctuations in water flow may cause nuisance
alarms. Additional green LEDs indicate higher flow rates, and
can avoid the nuisance alarms. Refer to Fig. 37.
1. Check to confirm that all strainers are clean, valves are
open and pumps are running. For the case of VFD
controlled pumps, ensure that the minimum speed setting
has not been changed.
2. Measure the pressure drop across the cooler and using
Appendix E on pages 95-100, calculate the cooler flow
and compare this to the system requirements.
3. If the measured flow rate through the cooler agrees with
the system requirements. At least 2 green LEDs should be
lit.
4. If the contacts do not close while two green LEDs are lit,
verify operation of the flow switch relay. Without chang-
ing fluid flow through the cooler, check for power at the
flow switch relay (FSR) coil. If power is not present,
check continuity of flow sensor cable. If the sensor cable
is not shorted or open when correct flow has been
confirmed and the green sensor LEDs are lit, the sensor
has failed and must be replaced.
OPT-A1
EPT-A
OPT-B1
SPT-A
EPT-B
SPT-B
DPT-B
DPT-A
Fig. 35A — 30HX Pressure Transducer Locations (2-Compressor Unit)
LEGEND FOR FIG. 35A-35C
DPT
— Discharge Pressure Transducer
EPT
— Economizer Pressure Transducer
EXV
— Electronic Expansion Valve
OPT
— Oil Pressure Transducer
SPT
— Suction Pressure Transducer
