6. When test has been completed, carefully reassemble EXV.
Be careful not to damage motor or O-ring when reassem-
bling valve. Open compressor service valves and close
compressor circuit breakers. Open liquid line service valve.
Turn control circuit switch to ON position, and allow unit
to operate. Verify proper operation of unit.
This process of opening and closing EXV can be repeated
by repeating quick test steps 3.5. or 3.9. and recycling
control as described in preceding steps. If valve does not
operate as described (when properly connected to processor
and receiving correct signals), replace valve.
If operating problems persist after reassembly, they may
be due to out-of-calibration thermistor(s), or intermittent con-
nections between processor board terminals and EXV plug.
Recheck all wiring connections and voltage signals.
Another possible cause of improper refrigerant flow con-
trol could be restrictions in liquid line. Check for plugged
filter drier(s), stuck liquid line solenoid valve(s), or re-
stricted metering slots in the EXV. Formation of ice or frost
on lower body of EXV is one symptom of restricted meter-
ing slots. Clean or replace valve if necessary.
NOTE: Frosting of valve is normal during quick test steps
3.5. and 3.9., and at initial start-up. Frost should dissipate
after 5- to 10-minute operation of a system that is operating
properly. If valve is to be replaced, wrap valve with a wet
cloth to prevent excessive heat from damaging internal
components. Superheat control built into valve is not
adjustable.
NOTE: The EXV orifice is a screw-in type that can be
removed 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
motor, lead screw, and the slide assembly up off the orifice
assembly. A slot has been cut in top of orifice assembly to
facilitate removal using a large screwdriver. Turn orifice as-
sembly 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 slide
and lead screw assembly out of the motor. Align hole in top
of slide with the guide pin in orifice assembly and gently
push slide 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 op-
eration in quick step steps outlined on page 44.
THERMOSTATIC EXPANSION VALVE (TXV) (080-110
ONLY) — The chiller with optional TXV is equipped with
2 conventional TXVs (one per circuit). This control system
necessitates use of a liquid line solenoid valve. TXVs are
factory set to maintain 8° to 10° F (4.4° to 5.6° C) superheat
of vapor leaving cooler by controlling flow of refrigerant into
cooler. Superheat can be reset but should be reset only if
absolutely necessary.
When optional TXVs are used, thermistors T5, T6, T7,
and T8 are eliminated (see Fig. 21).
The TXVs also incorporate an MOP (maximum operating
pressure) feature to limit cooler suction to 55 F (13 C), mak-
ing it possible for compressor to start at higher cooler fluid
temperatures without overloading.
NOTE: The TXV option is not available on 080-110 units
used as part of a modular system.
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
filter drier on each circuit. Refer to Carrier Standard Service
Techniques Manual, Chapter 1, Refrigerants, for details on
servicing filter driers.
LIQUID LINE SOLENOID VALVE — All units have a liq-
uid line solenoid valve to prevent liquid refrigerant migra-
tion 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
1
⁄
4
-in. Schrader
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 9 ther-
mistors to sense temperatures used to control the operation
of chiller. See Table 17.
Table 17 — Thermistor Designations
SENSOR TEMPERATURE
T1 Cooler Leaving Fluid
T2 Cooler Entering Fluid
T3 Saturated Condensing Temperature — Circuit A
T4 Saturated Condensing Temperature — Circuit B
T5* Evaporator Refrigerant Temperature — Circuit A
T6* Evaporator Refrigerant Temperature — Circuit B
T7* Compressor Return Gas Temperature — Circuit A
T8* Compressor Return Gas Temperature — Circuit B
T10 Remote Temperature Sensor (Accessory)
*Not used on units with optional TXV (080-110 only).
All thermistors are identical in their temperature vs re-
sistance and voltage drop performance. Resistances at vari-
ous temperatures are listed in Table 15 or 16.
LOCATION — General locations of thermistor sensors are
shown in Fig. 21.
Cooler Leaving Fluid Thermistor, T1 — Thermistor T1 is
located in the leaving fluid nozzle. The probe is in a well
immersed in the fluid. Actual location is shown in Fig. 21
and 23.
Cooler Entering Fluid Thermistor, T2 — Thermistor T2 is
located in the cooler shell in first baffle space, in close prox-
imity to tube bundle. The connection is made through
a
1
⁄
4
-in. coupling (Fig. 31). Actual location is shown in
Fig. 21 and 23.
65
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