Installation and Maintenance Manual
VAV-SVX07A-EN 69
Troubleshooting
• Disconnect the zone sensor terminal plug from the Tracer™ UC400 controller and using an
Ohmmeter, measure the resistance across the terminals 1 and 2. Compare the resistance to
temperature using Table 12, p. 69. The resistance should shown value should be within ± 2
degrees near those measured with an accurate temperature measuring device. If not, the
zone sensor needs to be replaced.
4. Verify that the wiring or the Tracer UC400 controller are not defective. With wires still connected
to the Tracer UC400 controller, disconnect zone sensor wires and check voltage (DC) from wires
that were connected to terminals 1 and 2 of zone sensor. You should measure 5VDC. If 5VDC
not present then see if the Tracer UC400 controller is outputting 5VDC. This can be done by
disconnecting the wires on the Tracer UC400 controller on terminals AI1 and and measure
the VDC. It should be 5VDC. If you have 5VDC at the Tracer UC400 controller the wires going
to the zone have an open. If 5VDC is not present check incoming power to the Tracer UC400
controller on XFMR 24 VAC input and should measure 24 VAC ± 10%. If you measure the
proper voltage at on XFMR 24 VAC input and and no voltage at AI1 and , replace the Tracer
UC400 controller.
5. Verify that the zone sensors are not shorted out. Check the resistance across the wires.
Disconnect wires from the Tracer UC400 controller and zone sensor making sure the ends are
not touching each other and measure resistance. It should be infinity or no conductivity. If lower
resistance is shown wires are shorted together and needs to be replaced.
Table 12. Zone sensor temperature resistance
Temp (
o
F) Thermostat Thumbwheel
Resistance (Ohms)
Sensor Resistance (k Ohms)
55
56
57
58
59
792
772
753
733
714
17.0
16.5
16.1
15.7
15.4
60
61
62
63
64
694
675
656
636
617
15.0
14.6
14.3
14.0
13.6
65
66
67
68
69
597
578
558
539
519
13.3
13.0
12.6
12.3
12.1
70
71
72
73
74
500
481
461
442
422
11.8
11.5
11.2
11.0
10.7
75
76
77
78
79
403
383
364
344
325
10.4
10.2
10.0
9.7
9.5
80
81
82
83
84
85
306
286
267
247
228
208
9.3
9.0
8.8
8.6
8.4
8.2
Note: Thumbwheel resistance checks are made at terminal 2 and 3 on the zone sensor. Temperature sensor resistance is
measured at terminal 1 and 2 of the zone sensor.