Ingersoll-Rand ReliaTel, Manual, Page: 152 / 176

152 RT-SVD03L-EN
ReliaTel ™ ™ - Condenser Fan
Control Logic - 12.5 to 25 Tons
For units that have two condenser fans, special control
logic is designed to provide proper condenser head
pressure control at different ambient conditions. With
normal operation, either one or both fans will be
operating depending on the outdoor temperature.
Control logic resides in the RTRM module. When the
outdoor ambient drops below 60 degrees the second
condenser fan will be turned off. When the outdoor
temperature reaches 65°, the fan will once again
restart.
When only one condenser fan is running, the second
fan will “windmill” backwards. This is caused by air
being drawn in through the opening of the fan orifice
which bypasses the condenser coil. If the windmilling
is fast enough and the condenser fan is energized, it
can actually start and run in the reverse direction. To
prevent this, when there is a call for the second
condenser fan to start, control logic forces the first
condenser fan to shut off for seven seconds to allow
the second fan to slow down. After seven seconds,
both the first and the second condenser fan will restart.
Because the contactors that provide power to the
condenser fan are also the same ones used to power
the compressors, both compressors (if the second
compressor is running) will also shut down during the
seven second interval. When the fans restart, the
compressor will also restart.
Sequence for eFlex ™ ™ Units
The same signal from the VSM that controls the
compressor speed also controls the speed of the
condenser fans. The condenser fan speed is
determined by the variable speed compressor speed
and the outdoor air temperature.
Sequencing Control - 27.5 to 50
Tons
The condenser fans are cycled according to the
outdoor air temperature and the number of cooling
steps that are operating. lists the temperatures at
which the A and B condenser fan outputs on the RTRM
switches the fans "Off". The fans are switched back
"On" when the outdoor temperature rises
approximately 5° F above the "Off" temperature.
Figure 98, p. 152 shows the condenser fans as viewed
from the top of the unit facing the control panel.
Whenever a condenser fan is cycled back "On", the
condenser fan outputs A and B and the compressor
steps are de-energized for approximately seven
seconds to prevent problems with fan windmill.
Figure 98. Condenser fan location
Lead Fan
Continuous Operation
Control Box