Dx Split-System Cooling - Trane Tracer AH540 Setup And Operation

Chapter 4 Sequence of operation
Table 25. Evaporator refrigerant temperature effect on DX cooling
Evaporator refrigerant temperature
Less than defrost setpoint.
Between defrost setpoint and defrost setpoint +10°F .
Greater than defrost setpoint +10°F .
66
temperature increases above the defrost setpoint + 10°F, an integrating
function is initiated. When the evaporator refrigerant time-temperature
satisfied, defrost operation is terminated. When defrost is terminated, DX
cooling capacity is allowed to once again stage On (see Table 25).
• DX cooling outputs will turn Off in sequence according
to a time-temperature function until the refrigerant tem-
perature rises above the defrost setpoint.
• DX cooling outputs stop unloading.
• Frosted DX cooling outputs will be re-enabled following
a minimum 10 minute defrost time interval.
• A time-temperature function will enable all compressor
stages.
Coil defrost binary input
The controller provides two binary inputs that can optionally be config-
ured for coil defrost, IN7 and IN12. These inputs should be used if the
universal analog input is not available or cannot be configured for evapo-
rator refrigerant temperature.
When the coil defrost binary input is active, the controller de-energizes
the last active DX cooling stage. All subsequent binary outputs will de-
energize; one stage every 120 seconds or until the coil defrost binary
input resets to a normal state.

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. In order 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,
condenser fan control, or periodic pump-out control. Pump-out and con-
denser fan control must be coordinated with condensing unit operation
using electromechanical 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 sequen-
tially 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 condens-
ing 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
DX cooling operation
CNT-SVX05B-EN