Saturated Condensing Temperature Thermistors, T3 and T4
— Thermistors T3 and T4 are each clamped to the outside
of a return bend on condenser coil. Exact locations for all
units are shown in Fig. 21 and 22.
Evaporator Refrigerant Thermistors, T5 and T6 — Ther-
mistors T5 and T6 are located next to refrigerant inlet in cooler
head. Thermistors are well-type thermistors. Typical loca-
tion is shown in Fig. 21 and 23. (Not used on units with
TXV.)
Compressor Return Gas Thermistors, T7 and T8 — Ther-
mistors T7 and T8 are located in lead compressor in each
circuit in a suction passage between motor and cylinders above
oil pump. They are well-type thermistors. Location is shown
in Fig. 21. (Not used on units with TXV.)
Remote Thermistor, T10 — Thermistor T10 is an accessory
and is mounted remotely from unit. It is used for outdoor air
or space temperature reset.
To troubleshoot a Thermistor, refer to separate Controls
and Troubleshooting literature.
TO REPLACE THERMISTOR T2 (Cooler):
Thermistor T2 is installed directly in the fluid circuit.
Relieve all pressure or drain fluid before removing.
1. Remove and discard original thermistor and coupling. Do
not disassemble new coupling. Install assembly as
received.
2. Apply pipe sealant to
1
⁄
4
-in. NPT threads on replacement
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 dis-
tance is
1
⁄
8
in. (3.2 mm) from cooler tube. Tighten pack-
ing nut finger-tight to position ferrules, then tighten
1
1
⁄
4
turns more using a back-up wrench. Ferrules are now
attached to the thermistor, which can be withdrawn from
coupling for service.
TO REPLACE THERMISTORS T1, T5, T6, T7, AND T8
— Add a small amount of thermal conductive grease to ther-
mistor well. Thermistors are friction-fit thermistors, which
must be slipped into receivers located in the cooler leaving
fluid nozzle for T1, in the cooler head for T5 or T6, and in
the compressor pump end for T7 or T8.
NOTE: Thermistor T1 is on all units; thermistors T5, T6,
T7, and T8 are on EXV units only.
THERMISTORS T3 AND T4 — These thermistors are lo-
cated on header end of condenser coil. They are clamped on
a return bend.
THERMISTOR/TEMPERATURE SENSOR CHECK — A
high quality digital volt-ohmmeter is required to perform this
check.
1. Connect the digital voltmeter across the appropriate
thermistor terminals at the J1 terminal strip on the pro-
cessor board (see Fig. 32 and Fig. 19). Using the vol-
tage reading obtained, read the sensor temperature from
Table 15 or 16. To check thermistor accuracy, measure
temperature at probe location with an accurate thermocouple-
type temperature measuring instrument. Insulate thermo-
couple to avoid ambient temperatures from influencing
reading. Temperature measured by thermocouple and tem-
perature determined from thermistor voltage reading should
be close, ± 5° F (3° C) if care was taken in applying ther-
mocouple and taking readings.
2. If a more accurate check is required, unit must be shut
down. Remove thermistor and check at a known tem-
perature (freezing point or boiling point of water) using
either voltage drop measured across thermistor at
the J1 terminals with unit in quick test mode
or
by determining the resistance with chiller shut down and
thermistor disconnected from J1.
FLUID-SIDE THERMISTOR (T1) AND
REFRIGERANT THERMISTORS
(T5, T6, T7, T8)
FLUID-SIDE THERMISTOR (T2)
NOTE: Dimensions in (
) are in millimeters.
Fig. 31 — Thermistors
LEGEND
COMPR — Compressor
*Not used on 080-110 units with optional TXV (thermostatic expan-
sion valve).
Fig. 32 — Thermistor Connections to J1,
Processor Board
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