Trane RTWA 70-125 TON - Manual (Page 19)

RLC-SVD03A-EN 19
Compressor Operation
This feature is called the Auto Lead/Lag and can be found in the Service
Settings Group, under the “Balanced CPRSR Starts and Hours” menu. When
this function is disabled, the UCM always starts compressor “A” first. When
this function is enabled, the following occurs:
The UCM equalizes operating starts and hours. This will cause the
compressor with the least amount of starts to be started first. When a
compressor starts, it is always started unloaded.
When a compressor is stopped, it shuts down in an unloaded state, unless
taken out by a manual reset diagnostic.
When the first compressor is brought on line, it attempts to meet the load by
staging on the step load solenoid and by pulsing the male slide valve load
solenoid. If one compressor cannot meet the load demand, the second
compressor is brought on line. It also attempts to meet the load demand by
staging on its step load solenoid and by pulsing its male slide valve solenoid.
When both compressors are running and both of their step load solenoids are
energized, the male load and unload solenoids on both compressors are
pulsed, thus modulating their respective slide valves to balance the load. The
UCM attempts to distribute the load evenly between the two compressors.
When the load drops off, the compressor with the most hours will always be
the first to unload and turn off. The anti-recycle timer is approximately 5
minutes from start to start. The minimum time between compressor
shutdown and restart is approximately 10 seconds, but only if the
compressor has been running over 5 minutes or longer prior to shutting down
on temperature. Otherwise, it is the remaining portion of the 5 minutes.
Restart Inhibit Timer
If compressor operation is interrupted by an extended (not momentary) loss
of power or a manual reset, there will be a two minute delay between the
power up or manual reset and the start of a compressor, assuming there is a
call for cooling. The timer is factory set at 2 minutes but can be field adjusted
from 30 seconds to two minutes in the Service Settings Group.