Trane LPC Install And Operation Instructions page 83

Table O-SO-12. Evaporator refrigerant temperature effect onDX cooling
DX split-system cooling
The Tracer AH540/541 controller
provides air-handling-unit, direct
expansion-cooling sequence of operation
for split-system air-handling units. For the
control system to operate, the controller
must be properly wired and configured to
the condensing unit.
The controller does not provide any lead-
lag, condensing unit protection, con-
denser fan control, or periodic pump-out
control. Pump-out and condenser fan
control must be coordinated with
condensing unit operation using electro-
mechanical devices.
Compressor stages and circuits
The Tracer AH540/541 controller
provides four 24 Vac binary outputs
(BO3 to BO6) for staged DX cooling. Each
output is energized sequentially BO3,
BO4, BO5, BO6 as cooling capacity
demand increases in a last-On, first-Off
method. To optimize the controller ability
to manage coil frost conditions, adhere to
the following staging and circuit
information when making wiring
connection between the controller and
the condensing unit.
For four-stage, two-circuit condensing
units connect BO3 to the first stage of
circuit 1, BO4 to the first stage of circuit 2,
BO5 to the second stage of circuit 1, and,
finally, BO6 to the second stage of circuit
2 (see Table O-SO-13).
Frost protection
The controller provides three options for
coil frost protection. Use the Rover
service tool to properly configure the
controller for the following options.
• Analog thermistor input (evaporator
LPC-SVX01C-EN
Operation
Table O-SO-13. DX cooling compressor circuit wiring
refrigerant temperature sensor) wired
to the universal analog input (IN13).
• Binary thermostat device wired to
binary input IN7, coil defrost input.
• Binary thermostat device wired to
binary input IN12, coil defrost input.
Two-circuit split-system DX cooling
applications should apply an evaporator
refrigerant sensor or binary thermostat
device on the first circuit or the circuit of
the first cooling stage.
For protection on each circuit both an
evaporator refrigerant sensor and binary
thermostat sensor or two binary thermo-
stat sensors can be used at the same
time. Apply a sensor to each circuit. The
controller will respond according to the
active input.
Also two binary thermostat devices can
be applied to each circuit and wired in
series to binary input IN7 or IN12. If either
sequence of
operation
device detects a low refrigerant tempera-
ture condition, the controller will enter a
defrost mode of operation.
Minimum On and Off timers
Remove (if installed), or disable, all
electromechanical compressor minimum
On and Off timers from the condensing
unit. The controller will enforce a
minimum On time and minimum Off time
for each compressor stage. A
compressor will not be allowed to stage
On until the compressor minimum Off
time has expired, and a compressor will
not be allowed to stage Off until the
compressor minimum On time has
expired.
Neglecting to remove or disable the
electromechanical timers will cause the
compressor operation to lose coordina-
tion with the controller compressor
staging control, and will result in poor
control performance.
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