Moisture-Liquid Indicator; Filter Drier; Liquid Line Solenoid Valve; Liquid Line Service Valve - Carrier 30GTN Service And Troubleshooting Manual

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ELECTRONIC EXPANSION VALVES (EXVs)
Fig. 29 — Printed Circuit Board Connector
NOTE: The EXV orifice is a screw-in type that can be re-
moved for inspection and cleaning. Once the top cover has
been removed, the EXV motor may be taken out by remov-
ing the 2 cap screws securing motor to valve body. Pull mo-
tor, lead screw, and the piston sleeve up off the orifice as-
sembly. See Fig. 28. A slot has been cut in top of orifice
assembly to facilitate removal using a large screwdriver. Turn
orifice assembly counterclockwise to remove.
When cleaning or reinstalling orifice assembly, be careful
not to damage orifice assembly seals. The bottom seal acts
as a liquid shut-off, replacing a liquid line solenoid valve.
Reassembly of valve is made easier by screwing the pis-
ton sleeve and lead screw assembly out of the motor. Align
hole in top of piston sleeve with the guide pin in orifice as-
sembly and gently push piston sleeve and lead screw onto
orifice assembly about half way. Screw motor onto lead screw
and secure EXV motor with cap screws. Be careful not to
twist or pull on wires from EXV motor to valve cover pin
connections. Check EXV operation using test functions de-
scribed in the Service Test section on page 29.
MOISTURE-LIQUID INDICATOR — Clear flow of liquid
refrigerant indicates sufficient charge in system. Bubbles in
the sight glass indicate undercharged system or presence of
noncondensables. Moisture in system measured in parts per
million (ppm), changes color of indicator:
Green — moisture is below 45 ppm;
Yellow-green (chartreuse) — 45 to 130 ppm (caution);
Yellow (wet) — above 130 ppm.
Change filter drier at first sign of moisture in system.
IMPORTANT: Unit must be in operation at least
12 hours before moisture indicator can give an accu-
rate reading. With unit running, indicating element must
be in contact with liquid refrigerant to give true
reading.
FILTER DRIER — Whenever moisture-liquid indicator shows
presence of moisture, replace filter drier(s). There is one fil-
ter drier on each circuit. Refer to Carrier Standard Service
Techniques Manual, Chapter 1, Refrigerants, for details on
servicing filter driers.
PL-EXVB
A
BRN
E
WHT
D
EXV-B
RED
B
BLK
C
GRN
PL-EXVA
A
BRN
E
WHT
D
EXV-A
RED
B
BLK
C
GRN
LIQUID LINE SOLENOID VALVE — All TXV units have
a liquid line solenoid valve to prevent liquid refrigerant mi-
gration to low side of system during the off cycle.
LIQUID LINE SERVICE VALVE — This valve is located
immediately ahead of filter drier, and has a
connection for field charging. In combination with compres-
sor discharge service valve, each circuit can be pumped down
into the high side for servicing.
Thermistors —
Electronic control uses 4 to 10 ther-
mistors to sense temperatures used to control the operation
of chiller.
Thermistors T1-T9 are identical in their temperature vs
resistance and voltage drop performance. Thermistor T10 is
a 10 k input channel and has a different set of temperature
vs resistance and voltage drop performance. Resistances at
various temperatures are listed in Tables 30A-31B.
LOCATION — General locations of thermistor sensors are
shown in Fig. 7-10. See Table 2 for pin connection points.
Sensor T2 is installed directly in the fluid circuit. Re-
lieve all pressure or drain fluid before removing.

REPLACING THERMISTOR T2

1. Remove and discard original sensor and coupling. Do not
disassemble new coupling. Install assembly as received.
See Fig. 30.
2. Apply pipe sealant to
coupling, and install in place of original. Do not use the
packing nut to tighten coupling. Damage to ferrules will
result.
3. Thermistor T2 (entering fluid temperature) should not be
touching an internal refrigerant tube, but should be
close enough to sense a freeze condition. Recommended
distance is ⁄ in. (3.2 mm) from cooler tube. Tighten pack-
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8
ing nut finger tight to position ferrules, then tighten
1 1 ⁄ turns more using a back-up wrench. Ferrules are now
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attached to the sensor, which can be withdrawn from cou-
pling for service.
FLUID-SIDE TEMPERATURE SENSOR (T1) AND
REFRIGERANT TEMPERATURE SENSOR (T5, T6, T7, T8)
FLUID-SIDE TEMPERATURE SENSOR (T2)
NOTE: Dimensions in ( ) are in millimeters.
Fig. 30 — Thermistors (Temperature Sensors)
57
⁄ -in. Schrader
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4
1 ⁄ -in. NPT threads on replacement
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