Trane VAV-UCM 4.2 - Page 69

VAV-SVX01C-EN 69
Troubleshooting
• When calibration is complete, the box will release to auto. Drive the box open to make sure
that the box is not below 5% of its cataloged CFM. The controller is accurate in reading flow
from 5% to 110% of cataloged CFM.
• Release the box to auto and perform any necessary balancing work. See “A i r a n d Wa t e r
Balancing,” p. 54 for details.
• Check to see if flow has been established, If flow not established or inaccurate proceed
to Step 2.
2. The tubing or flow ring is off, reversed, plugged, or has a leak.
• Check with a magnehelic gauge and compare with the delta pressure (DP) chart located on
the VAV box.
• Check the tubing for reversal and/or leaks.
• Check the flow ring for plugged holes. Blow out with compressed air if necessary.
3. Wrong unit size downloaded into the UCM setup menu
• Verify that the actual unit size matches the unit's nameplate.
4. Poor inlet configuration
• Trane recommends 1½-duct diameters of straight duct before the inlet of the box (a 12-inch
box should have 18” of straight run duct before the inlet).
5. To determine whether or not the transducer has failed, perform the following steps:
• Check the 24 volts AC supply at TB1-1 and TB1-2 on the UCM board. Voltage should be
between 20 volts AC and 28 volts AC. If voltage not available see UCM failure procedures.
• Read the input voltage to the transducer from the UCM controller between the green and red
wires on J3 of the UCM board. The voltage should be between 4.50 volts DC and 5.50 volts
DC (5 volts DC cataloged). If voltage not available replace UCM.
Figure 39. Sensor signal vs. airflow delivery
0.01
0.1
1
5
10 100 1,000 10,000
Cfm
Flow Sensor DP (In . w g )
4"
12"10"8"6"
5"
14"16"