Transducer Troubleshooting; Forcing Inputs And Outputs - Carrier 48PG03-16 Controls, Start-Up, Operation, Service And Troubleshooting Instructions

Refrigerant Temperatures
Condenser coil temperatures are measured with 5 kilo-ohm
thermistors. These measurements provide an approximate
saturated condensing temperature for each circuit (SCT.A, SCT.B,
SCT.C). Fig. 19- -21 show the factory locations for the SCT
thermistors. 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.
Fig. 18 --- SAT and OAT Thermistor Mounting
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 section).
Using the voltage reading obtained, read the sensor temperature
from Tables 99 and 100.
To check thermistor accuracy, measure temperature at probe
location with an
temperature-measuring instrument. Insulate thermocouple to
avoid ambient temperatures
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
determining the resistance with unit shut down and thermistor
disconnected from J8. Compare the values determined with the
value read by the control in the Temperatures mode using the
Scrolling Marquee display.
C07015
accurate thermocouple-type
from influencing reading.
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→ TRIM menu for the display, or 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. Temperature
corrections should only be made if sensor readings are compared
to an accurate reference temperature measurement device.

Transducer Troubleshooting

The electronic control uses suction pressure transducers to
measure the suction pressure of the refrigerant circuits. The
pressure/voltage characteristics of these transducers are in shown
in Table 101. The accuracy of these transducers can be verified by
connecting an accurate pressure gauge to the second refrigerant
port in the suction line.

Forcing Inputs and Outputs

Many variables may have their value forced through CCN or
directly at the local display. This can be useful during diagnostic
testing and also during operation, typically as part of an advanced
third party control scheme. Input and output points that may be
forced are indicated as 'forcible' in the write status column of the
display and CCN tables.
If the user needs to force a variable, follow the same process as
when editing a configuration parameter. A forced variable will be
displayed on the Scrolling Marquee with a blinking period "."
following its value. A forced value on Navigator™ accessory is
indicated with a blinking "f". A forced value on CCN devices is
indicated with "Control" if forced at the unit display, or
"Supervisor" if forced via CCN. To remove a local force with the
Scrolling Marquee, select the point with the ENTER key and then
press the up-arrow and down-arrow keys simultaneously.
NOTE: In the case of a control power reset, any force in effect at
the time of power reset will be cleared.
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