Trane RTHD Troubleshooting Manual page 25

RLC-SVD05A-EN
Variable Speed Fan Control - RTAC Only
Note: The output from the compressor LLID is a pulse width modulated signal, 10
volt peak and 10 Hz. fundamental. Its average value can be read with a DC
voltmeter.
7 Remove the jumper wire and reconnect connector P1 or P2. While the inverter
is still powered, measure the DC voltage between pins F (+) and FR (-) on the
Dual Inverter Interface LLID. The connector must be plugged on at both ends
while measuring this voltage. If the reading is between 11.5 and 12.5 VDC two
problems may exist:
a The inverter indicates that it has a fault by opening a semiconductor switch
within the inverter. The inverter sends a fault signal to the MP 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 diagnostic trip.
– The output frequency of the inverter is being internally limited to less
than 50% of the signal speed commanded by the MP . Excessive fan
motor current, high temperature or internal inverter failures could cause
this to occur.
b 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 F and FR, an inverter fault diagnostic for
the affected circuit should not be displayed. 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 Dual
Inverter Interface LLID a fault signal if these two wires are shorted together.
8 If all the settings and voltages through step 7 are acceptable and the fan does
not operate, replace the variable speed fan inverter.
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