58 VAV-SVX07F-EN
Troubleshooting
Supply/Discharge Air Temperature Sensor Failure
WARNING
Hazardous Service Procedures!
The maintenance and troubleshooting procedures recommended in this section of the manual
could result in exposure to electrical, mechanical or other potential safety hazards. Always
refer to the safety warnings provided throughout this manual concerning these procedures.
When possible, disconnect all electrical power including remote disconnect and discharge all
energy storing devices such as capacitors before servicing. Follow proper lockout/tagout
procedures to ensure the power can not be inadvertently energized. When necessary to work
with live electrical components, have a qualified licensed electrician or other individual who
has been trained in handling live electrical components perform these tasks. Failure to follow
all of the recommended safety warnings provided, could result in death or serious injury.
In the event that the UC400 controller reports an i
ncorrect
or failed discharge or supply air
temperature, check the following:
• Ensure the UC400 controller has been configured for the input and the po
int has not been
placed out of service.
• Discharge or supply air temperature is higher or lower than what
the UC400 controller
reads.
• Check the location and installation of th
e sensor. Change the calibration factor in the UC400
controller setup screens.
Note: If sensor is off more than ± 2 degrees continue to the next bullet.
• Ch
eck sensor wiring for the correct connections.
• Defe
ctive sensor.
– Disconnect the sensor terminal plug from the UC40
0 controller and using
an ohmmeter,
measure the resistance across the sensor wires. Compare the resistance to temperature
(refer to Table , p. 54). The resistance measured should correspond to a temperature within
± 2 degrees nea
r those measured with an accurate temperature measuring device. If the
measured resistance does not correspond, replace the sensor.
• Defective wiring or defective UC400 contro
ller.
– Verify that the UC400 controller is outputting 2.6–3.0 Vdc. Th
is can be performed by
disconnecting the wires on the UC400 controller on terminals AI4 and for a discharge air
temperature sensor, or AI5 and for a supply air temperature sensor, and measuring the
Vdc. It should be 5 Vdc. If there is 2.6–3.0 Vdc at the UC400 controller, the wires going to the
zone are OPEN. If 5 Vdc is not present, check the incoming power to the UC400 controller
on XFMR 24 Vac input and . It should measure 24 Vac ± 15%. If the proper voltage is
measured at XFMR 24 Vac input , and there is no voltage at AI4 and for discharge air
temperature sensor or AI5 and for supply air temperature sensor, replace the UC400
controller.
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