Thermistors; Thermistor Replacement; Pressure Transducers; Pressure Transducer Calibration - Carrier Ecologic Series 3 Controls, Start-Up, Operation, Service, And Troubleshooting

Thermistors —
To aid in verifying thermistor perfor-
mance, resistances at various temperatures are listed for all
thermistors (except motor thermistors) in Tables 42A and 42B.
See Table 43 for motor thermistor values.
LOCATION — General location of thermistor sensors and ter-
minal connections in the control box are listed in Table 2.

THERMISTOR REPLACEMENT

Liquid level thermistors are installed in the top of the
cooler using compression fittings. All other thermistors are
installed in wells and will slide out of the wells easily. The
wells are under refrigerant pressure (cooler EWT and LWT
are under waterside pressure) and do not need to be
removed to replace a faulty thermistor.
To replace thermistors T1, T2, T5, or T6 (Entering, Leaving
Water; Discharge Gas Temperature):
Disconnect appropriate wires from PSIO-2 in unit control
box. Remove thermistor cable from harness. Remove and dis-
card original thermistor from well. Insert new thermistor in
well body to its full depth. Add a small amount of thermal con-
ductive grease to thermistor probe and well. Thermistors are
friction-fit thermistors and will slip back into well located at
the cooler head (T1, T2) or at the top of the condenser shell
(T5, T6). Secure thermistor to well body with a wire tie to
prevent thermistor from working its way out of the well. See
Fig. 22.
To replace thermistors T3 or T4 (Liquid Level Sensors):
See the Inspecting/Opening Economizers section on
page 53 for information on transferring the refrigerant charge
to the high side. Transfer refrigerant and recover any refriger-
ant 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 all units, disconnect plug assembly at liquid level sen-
sor. Loosen the packing nut fully from the well threads. Re-
move and discard old thermistor and packing nut. Slide new
packing nut then ferrule up onto new thermistor probe from in-
serted end. Insertion depth is dependent on unit model number.
See Fig. 23 and Table 44.
Hand tighten packing nut to position ferrule while holding
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. Re-
connect blue wires at PSIO-1 for thermistor reading and red
wires to TRAN-7. Reconnect plug assembly to new liquid lev-
el sensor for 30GX205-265 units. Restore unit control power
only and verify that level thermistor is reading 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 compressor
junction box. There are 3 terminals for the thermistors: S1, S2,
and C. Motor temperature is measured by leads connected to
one of the S terminals and the C terminal. If a compressor mo-
tor 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 43 for motor thermistor temperature and resistance
values.
Pressure Transducers —
transducer is used for both high- and low-pressure sensing on
A single style of pressure
the 30GX,HX chillers. The transducers operate on a 5 vdc sup-
ply. The power supply for this is a 24 vac to 5 vdc full wave
rectified power supply, PS1. See unit component arrangement
label for mounting location and terminal connections in the
control box. Refer to Fig. 24A and 24B 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 transducer
when the system is under nitrogen charge will result in an
incorrect offset being applied to the reading (due to tempera-
ture correction). Although these transducers are calibrated at
the factory, replacement transducers require calibration 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 45, 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 45.
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 overtighten the transducer
when replacing after calibration. Hold both fittings with
wrenches when removing and reinstalling.
The control will apply the 0.8 psi offset from the calibration
example in Table 45 to all future readings. The calibration pro-
cess for any of the other pressure transducers is done in a simi-
lar manner. A transducer can also be calibrated at atmospheric
pressure by removing the transducer from the system. To do
this, carefully unplug the transducer connector. Unscrew the
transducer from its mounting location and reconnect the con-
nector. Follow the steps in Table 45 to read the current pressure
and enter 0.0 psig as the gage pressure. Remove the connector
from the transducer, thread the transducer back onto the fitting
from which it was removed (do NOT use thread sealant/com-
pound), and reinstall the connector. Maximum offset is 6 psig.
If it is necessary, all of the transducers may be calibrated at
0.0 psig. All of the transducers must be removed from the sys-
tem and reconnected in atmosphere as described. When com-
plete, scroll down under
and press. A "Yes" will be displayed at this step and will auto-
matically change back to "No" once all transducers have been
successfully calibrated. Reconnect the transducers and connec-
tors 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 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.
61
to "Calibrate All at 0 PSIG"