Trane RTWA 70-125 TON - Manual (Page 84)

84 RLC-SVD03A-EN
Variable Speed Fan System
on at both ends while measuring this voltage. If the reading is between
11.5 and 12.5 VDC, two problems may exist:
• The inverter indicates that it has a fault by opening a semiconductor
switch within the inverter. The inverter will send a fault signal to the UCM
when:
– It has gone through a self-shutdown. One cause of this could be
high line voltage. A 10% high line voltage could cause a diagnos-
tic trip.
– The output frequency of the inverter is being internally limited to
a less than 50% of the signal speed commanded by the UCM.
Excessive fan motor current, high temperature or internal inverter
failures could cause this to occur.
• There is an open circuit in the fault signal wiring, somewhere between
the inverter and the compressor module.
If the reading is 2 VDC or less between pins J9-4 and J9-3, an inverter fault
diagnostic for the affected circuit should not be displayed. But if the variable
speed fan in still not working, check these two interconnecting wires from
the compressor module to the inverter, to be sure they are not shorted. The
inverter cannot send the compressor module a fault signal if these two wires
are shorted together.
9. If all settings and voltages through Step 8 are acceptable and the fan
does not operate, replace the variable speed fan inverter.