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to the high side. Transfer refrigerant and reclaim any refrig-

erant remaining in the low side.

NOTE: A new packing nut and ferrule will be required as

the old one is not removable from the old thermistor.

For 30GX080-176 and all 30HX units cut wire nuts apart

to appropriate blue leads at PSIO-1 (J7-5,6 for T3; J7-8,9 for

T4) and red leads connecting wires to TRAN-7. Remove old

leads from control box harness. For 30GX205-265 units, dis-

connect plug assembly at liquid level sensor. Loosen the pack-

ing nut fully from the well threads. Remove and discard old

thermistor and packing nut. Slide new packing nut then fer-

rule up onto new thermistor probe from inserted end. Inser-

tion depth is dependent on unit model number. See Fig. 22

and Table 41.

Hand tighten packing nut to position ferrule while hold-

ing thermistor in position. With wrench, tighten enough to

ﬁrmly secure thermistor in place in well. Run new harness

wires into main control box for 30GX080-176 and all 30HX

units. Reconnect blue wires at PSIO-1 for thermistor read-

ing and red wires to TRAN-7. Reconnect plug assembly to

new liquid level sensor for 30GX205-265 units. Restore unit

control power only and verify that level thermistor is read-

ing correctly. Check system low side for leaks and repair as

necessary. Evacuate low side and open circuit discharge and

liquid valves.

To service compressor motor thermistors:

Two thermistors are factory installed in each compressor.

Connections for the thermistors are located in the compres-

sor junction box. There are 3 terminals for the thermistors:

S1, S2, and C. Motor temperature is measured by leads con-

nected to one of the S terminals and the C terminal. If a com-

pressor motor thermistor failure occurs, verify that there is

a true short or open circuit at these terminals. If one of the

thermistors fails, disconnect and relocate the wire on one of

the S terminals to the other S terminal (S1 to S2 or S2 to S1).

The thermistors are not serviceable in the ﬁeld. If both of the

compressor motor thermistors fail, compressor replacement

is required. See Table 40 for motor thermistor temperature

and resistance values.

Pressure Transducers — A single style of pressure

transducer is used for both high- and low-pressure sensing

on the 30GX,HX chillers. The transducers operate on a

5 vdc supply. The power supply for this is a 24 vac to

5 vdc full wave rectiﬁed power supply, PS1. See unit com-

ponent arrangement label for mounting location and termi-

nal connections in the control box. Refer to Fig. 23A and

23B for pressure transducer locations.

PRESSURE TRANSDUCER CALIBRATION — Pressure

transducers are factory installed on all models to read Dis-

charge, Suction, Economizer (reads leaving condenser pres-

sure on models without economizer), and Oil pressure. DO

NOT attempt to calibrate any of these transducers by the pres-

sure gage method unless the transducer is connected to a fully

charged refrigerant system. A more accurate method of cali-

bration is used by the 30GX,HX software and corrects for

ambient temperature when calibrating. Calibrating a trans-

ducer when the system is under nitrogen charge will result

in an incorrect offset being applied to the reading (due to

temperature correction). Although these transducers are cali-

brated at the factory, replacement transducers require cali-

bration for accurate readings. Calibration is also required when

replacing a PSIO. Access to the transducer calibration area

is through the Service function and the transducers can

be calibrated at the current system pressure using a pressure

gage at the same point or exposed to atmospheric pressure.

In the example in Table 42, the Circuit A Discharge Pressure

transducer has been replaced and needs to be calibrated. A

pressure gage has been installed at the transducer and reads

85 psi (must be in the range of −5.0 to 185.0 psi). See

Table 42.

Use care when removing the oil pressure transducers from

the compressor ﬁtting. The ﬁtting that the transducers

mount in is sealed with an O-ring Schrader ﬁtting into

the compressor casting. Do NOT overtigthen the trans-

ducer when replacing after calibration. Hold both ﬁt-

tings with wrenches when removing and reinstalling.

The control will apply the 0.8 psi offset from the calibra-

tion example in Table 42 to all future readings. The cali-

bration process for any of the other pressure transducers is

done in a similar manner. A transducer can also be calibrated

at atmospheric pressure by removing the transducer from the

system. To do this, carefully unplug the transducer connec-

tor. Unscrew the transducer from its mounting location and

reconnect the connector. Follow the steps in Table 42 to read

the current pressure and enter 0.0 psig as the gage pressure.

Remove the connector from the transducer, thread the trans-

ducer back onto the ﬁtting from which it was removed (do

NOT use thread sealant/compound), and reinstall the

connector.

If it is necessary, all of the transducers may be calibrated

at 0.0 psig. All of the transducers must be removed from the

system and reconnected in atmosphere as described.

When complete, scroll down under to ‘‘Calibrate

All at 0 PSIG’’ and press . A ‘‘Yes’’ will be dis-

played at this step and will automatically change back to ‘‘No’’

once all transducers have been successfully calibrated. Re-

connect the transducers and connectors as described above.

All transducers are mounted on Schrader ﬁttings. Therefore,

it is NOT necessary to remove system refrigerant charge.

Use a catch pan when removing the oil pressure transducer

for calibration as oil will leak out through the Schrader

ﬁtting.

TROUBLESHOOTING — If transducer is suspected of be-

ing 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.

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