Trane RTWA 70-125 TON - Manual (Page 22)

22 RLC-SVD03A-EN
Variable Speed Inverter/
Condenser Fan Control
speed will also cause constant speed fans to stage On and Off when the
inverter is commanded to full speed and minimum speed respectively. The
stage On (or Off) of a constant speed fan will occur if the inverter speed
command is at max (or min.) for three consecutive intervals (15 seconds).
Outdoor Air Temperature and Fan Control
Outdoor air temperature is used to provide a reasonable startup state. Using
this temperature, the algorithm automatically determines the number of
constant speed fans to turn on immediately at compressor start. The outdoor
air temperature sensor is also used to anticipate new states during normal
running to minimize pressure upsets. This anticipation is based on the staging
and unstaging of compressor steps at given leaving water temperatures. In
this way, precise airflow can be maintained, allowing for stable differential
pressures under part load and low ambient conditions.
VSF Inverter Fault
A fault signal will be sent to the UCM from the Inverter when it has gone
through a self-shutdown or if the output frequency of the Inverter is being
limited to less than 50% of the signal speed commanded by the UCM. Upon
receipt of the fault signal, the UCM shall attempt to reset the fault by sending
a 0 PWM command to the Inverter for a total of five seconds. The fault signal
will again be checked and repeated if still in fault. If four faults are detected
within one minute of each other, the power to the Inverter will be cycled off
for 30 seconds (through contactor control) and then re-powered. If the fault
still remains or occurs again within one minute, an IFW diagnostic occurs.
The UCM will remove power from the Inverter and attempt to run the
remaining constant-speed fans using normal constant-speed Fan Control
Algorithm. See page 80 for step-by-step troubleshooting procedure.