Operation; Units With Evaporative Condenser; Sequence Of Operation - Trane IntelliPak 2 Series Installation, Operation And Maintenance Manual

When the compressor starts, the sudden reduction in
crankcase pressure causes the liquid refrigerant to boil
rapidly causing the oil to foam. This condition could
damage compressor bearings due to reduced
lubrication and could cause compressor mechanical
failures.
Low Ambient Compressor Operation
Certain applications require compressor operation at
lower ambient conditions than standard units. Low
ambient compressor operation is a factory configured
option that allows units to operate down to -10°F by
extending the low ambient compressor lockout
setpoint range.
Standard configuration units are limited to a minimum
low ambient compressor lockout setpoint of 40° F. In
conditions below 40°F the low-pressure cutout (LPC)
switch can open in the first few minutes of initial
compressor operation due to refrigerant circulation
characteristics. To prevent nuisance LPC events at
start-up in these conditions the unit controller will
bypass LPC processing for a varying period of time as
defined below:
• For ambient temps below 20°F LPC events will be
bypassed for the first 170 seconds of compressor

operation.

• For ambient temps between 20° and 40°F the
bypass time reduces linearly from 170 seconds at
20°F to 0 seconds at 40°F. LPC events are not
bypassed at initial compressor start in ambient
conditions above 40°F.
170
0
0F
Outdoor Air Temp (°F)
• An open LPC switch detected at compressor start
will result in a manual-reset compressor lockout
condition.
• 4 consecutive LPC trip occurrences after the bypass
time expires without a minimum of 3 minutes of
compressor operation between trips will result in a
manual-reset compressor lockout.
In addition to alternate LPC event processing, the
second compressor to start on each refrigerant circuit
will be disabled for 40 minutes each time a circuit starts
in ambient conditions less than 40°F. To properly
maintain head pressure control in low ambient
conditions one condenser fan on each refrigerant
RT-SVX24Q-EN
20F 40F
circuit will be controlled by a Variable-frequency motor
drive (VFD).
This fan will always be the first fan active. The VFD will
control fan speed at all times compressors are active to
the HI-adjustable Low Ambient Control Point. If head
pressure control requires additional condenser fan
stages to maintain proper Saturated Condenser
Temperature within limits they will be activated as
necessary according to the standard head pressure
control fan-staging algorithm.

Units with Evaporative Condenser

Sequence of Operation

Upon a power up without water in the sump, the
condenser sump drain will be controlled to allow the
sump to hold water. The fill relay will be energized if
there is a call for mechanical cooling and if the outdoor
air temperature is greater than 10°F on units with a
sump heater installed or greater than 40°F on units
without sump heat. Once the fill solenoid is energized,
the sump will begin to fill. The minimum water level
switch will close and the fill relay will be de-energized.
The sump water temperature sensor is invalid unless
the minimum water level switch is closed.
If the sump water temperature is less than the setpoint
(default is 38°F), the sump heater will be energized until
the water temperature reaches the setpoint plus 5
degrees (43°F for default). The fill solenoid will remain
closed for 20 minutes or until the water temperature is
greater than 35°F. Once a water temperature of 35°F or
greater is achieved, the fill solenoid is energized, the
sump will continue to fill, and a five minute timer is
started.
When the timer expires, the compressor lockout will be
released and mechanical cooling will be allowed. Head
pressure control will be regulated by a variable speed
fan until the liquid line pressure from either circuit
reaches the upper limit, which is set on the Human
Interface under the setup menu 120°F default. The
liquid line pressure is converted to a temperature for
display at the Human Interface. When the temperature
exceeds the upper limit, the condenser sump pump will
be energized. When the sump pump is energized,
water is pumped from the sump and sprayed over the
condenser coil. If the liquid line pressure from either
circuit falls below the lower limit the sump pump will
be de-energized.
When the sump pump is energized or de-energized a
change in state is observed from an auxiliary contactor
to ensure proper sump pump operation. A change in
states must be observed by the auxiliary contactor
within 6 seconds of the command to change states or
mechanical cooling will be locked out on a sump pump
failure causing a manual reset diagnostic to be set.
The fill solenoid will remain energized and the water
level will be controlled by the mechanical float valve. If
the maximum level float ever closes, an information-
only diagnostic is set and the fill solenoid is de-
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