Trane RTHD Troubleshooting Manual page 24

24
Variable Speed Fan Control - RTAC Only
3 Attempt to start the compressor on the desired circuit. Thirty seconds prior to
compressor start, the variable speed fan inverter contactor is energized. Be
sure that you can hear the fan contactor pull in. If not, attach an AC voltmeter
from FR to ground on the Dual Inverter Interface LLID. Reset the control and
look for a 115 volt reading on the voltmeter at FR, 25 to 30 seconds prior to
compressor start. If this 115 volts is verified but the contactor does not pull in,
check for an open circuit in the contactor coil or an open circuit in the
interconnecting wiring to the contactor.
4 Check the fan motor by completely bypassing the inverter. Disconnect power
from the chiller and remove the three-phase power wiring from the inverter.
Connect it to the three-phase power wiring of the fan motor. Re-apply power
to the unit and reset the circuit being tested. Make sure the phasing is proper
when reconnecting the inverter. Twenty-five or thirty seconds before the
compressor starts, the contactor that would normally apply power to the
inverter should pull in and the fan should run. If the fan does not run, check
the line fuses and contactor contacts.
The fan will only run for approximately 30 seconds before the inverter fault
will cause the contactor to drop out.
5 Disconnect power from the unit and reconnect the inverter module. At the
same time, check for damaged wiring or loose quick connects on the inverter.
6 Remove connector P1 or P2 (whichever applies) from the inverter and place a
jumper wire between terminals F and FR on the female connector. See
Figure 12 for the location of these wires. This will prevent the control from
reporting a fault diagnostic. Restart the unit and carefully measure the DC
voltage between wires C (+) and CR (-) on the same female connector. The
voltage should be 2 to 10 VDC when the compressor on the affected circuit is
running. At compressor start, this voltage will be approximately 2 VDC and
gradually ramp up to about 10 VDC. This voltage level is directly proportional
to fan speed. At 5 VDC, the fan should be running at 50% of full speed and at 7
VDC the fan should be running at 70% of full speed.
Figure 12.Variable Speed Fan Inverter
RLC-SVD05A-EN