Carrier 50PG20-28 Controls, Start-Up, Operation, Service And Troubleshooting Instructions page 64

Fig. 13 -- SAT and OAT Thermistor Mounting
Ifa more accurate check is required, unit must be shut do,a_
and therlnistor relnoved and checked at a kalo,a_ telnperature
(freezing point or boiling point of water) using either voltage
drop measured across therlnistor at the J8 terlninal, or by deter-
mining the resistance with unit shut down and therlnistor
disconnected fiom J8. Colnpare the values deterlnined with the
value read by the control in the Telnperatures mode using the
Scrolling Marquee display.
SENSOR TRIM Corrective oit;ets can be applied to the
space temperature and the supply air temperature sensor
readings. These corrections are set in the Configm,ation--+
TRIM menu for the display, or in the Maintenanee-+TRIM
table for CCN. See the Indoor Air Quality section ibr available
adjustments to IAQ and OAQ sensor readings. The space
temperature may be COlTectedby entering either a calibration
temperature value in SPT.C, or an oit;et temperature value in
SPT.Z The supply-air temperature may be corrected by enter-
ing either a calibration temperature value in SAT.C, or an oit;et
temperature value in SAT.!] Telnperamre corrections should
only be made if sensor readings are compared to an accurate
reference temperature measurelnent device.
Transducer Troubleshooting
-- The electronic con-
trol uses salction pressure transducers to measure the suction
pressure of the refrigerant circuits. The pressure/voltage char-
acteristics of these transducers are in sho,a_ in Table 52. The
accuracy of these transducers can be verified by connecting
an accurate pressure gage to the second refiigerant 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 diamaostic testing and also
during operation, typically as part of an advanced third party
control scheme.
Input
and output points that may be tbrced 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 paralneter. A forced variable
will be displayed on the Scrolling Marquee with a blinking
period "." following its value. A forced value on Navigator
TM
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 relnove a local
tbrce 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 tbrce in effect
at the time of power reset will be cleared.
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