Refrigerant Temperatures; Thermistor/Temperature Sensor Check; Sensor Trim - Carrier 48HC 04-28 Controls, Start-Up, Operation And Troubleshooting

Fig. 18 — SAT and OAT Thermistor Mounting

REFRIGERANT TEMPERATURES

Condenser coil temperatures are measured with 5 kilo-ohm
thermistors. These measurements provide an approximate satu-
rated condensing temperature for each circuit (SCT.A, SCT.B).
Figures 19-23 show the factory locations for the SCT thermis-
tors. Ensure that thermistors are placed at the correct location
and are snapped securely over the return bend so that contact is
made between the thermistor and the tube.

THERMISTOR/TEMPERATURE SENSOR CHECK

A high quality digital volt-ohmmeter is required to perform
this check.
Connect the digital voltmeter across the appropriate thermistor
terminals at the J8 terminal strip on the Main Base Board (see
Major System Components on p. 68).
Using the voltage reading obtained, read the sensor tempera-
ture from Tables 22 and 23.
To check thermistor accuracy, measure temperature at probe
location with an accurate thermocouple-type temperature-mea-
suring instrument. Insulate thermocouple to avoid ambient
temperatures from influencing reading. Temperature measured
by thermocouple and temperature determined from thermistor
voltage reading should be close, within 5°F if care was taken in
applying thermocouple and taking readings.
If a more accurate check is required, unit must be shut down
and thermistor removed and checked at a known temperature
(freezing point or boiling point of water) using either voltage
drop measured across thermistor at the J8 terminal, or by deter-
mining the resistance with unit shut down and thermistor dis-
connected from J8. Compare the values determined with the
value read by the control in the Temperatures mode using the
scrolling marquee display.

SENSOR TRIM

Corrective offsets can be applied to the space temperature and
the supply air temperature sensor readings. These corrections
are set in the Configuration

in the Maintenance TRIM table for CCN. See the Indoor Air
Quality section for available adjustments to IAQ and OAQ
sensor readings. The space temperature may be corrected by
entering either a calibration temperature value in SPT.C, or an
offset temperature value in SPT.T. The supply-air temperature
may be corrected by entering either a calibration temperature
value in SAT.C, or an offset temperature value in SAT.T. If in-
stalled, the return air temperature may be corrected by entering
either a calibration temperature value in RAT.C, or an offset
temperature value in RAT.T. Temperature corrections should
only be made if sensor readings are compared to an accurate
reference temperature measurement device.
58

TRIM menu for the display, or