Staged Dx Cooling; Defrost Operation - Trane Tracer AH540 Setup And Operation

CNT-SVX05B-EN

Staged DX cooling

One to four DX cooling stages can be directly controlled from binary out-
puts. Since the controller binary outputs can also be configured for stages
of electric heat the binary outputs are assigned as follows where the num-
ber of DX cooling stages plus the number of electric heat stages cannot
exceed four outputs.
BO3: DX cooling stage 1 or Electric heat stage 4
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BO4: DX cooling stage 2 or Electric heat stage 3
•
BO5: DX cooling stage 3 or Electric heat stage 2
•
BO6: DX cooling stage 4 or Electric heat stage 1
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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 Of until the compressor minimum On time has
expired. See Table 39 on page 77.
Inter-stage delays are also enforced. A minimum of 3 minutes will be
enforced between additional cooling stages. A minimum of 2 minutes will
be enforced between subtracting cooling stages.

Defrost operation

Low evaporator refrigerant temperatures can cause the coil to frost. The
Tracer AH540/541 controller provides two methods of detecting low evap-
orator refrigerant temperatures:
One uses the evaporator refrigerant temperature (analog input IN13)
•
to measure suction temperature
The other uses a binary thermostat device (binary input IN7 or IN12)
•
applied to the evaporator suction line
Two-circuit split-system DX cooling applications should provide an evapo-
rator refrigerant sensor or binary thermostat device on the first circuit or
the circuit with the first cooling stage. As an option, both an evaporator
refrigerant sensor and binary thermostat can be used on a unit with one
device installed on each circuit. The controller will respond according to
either frost input.
Two binary thermostat devices can also be used with one device installed
on each circuit. The devices are separately hard-wired to coil defrost
inputs IN7 and IN12, or the thermostat devices are wired in series to coil
defrost input IN7 or IN12.
Evaporator refrigerant temperature
A 10 kΩ thermistor can be hard-wired to the universal analog input IN13.
The controller has the ability to directly measure the evaporator refriger-
ant temperature. If evaporator refrigerant temperature drops below the
defrost setpoint (30°F, default) the controller will unload one compressor
stage every 120 seconds. If the refrigerant temperature rises above the
defrost setpoint, DX cooling will stop unloading and each stage that
frosted will be enabled after a minimum of 10 minutes. If the refrigerant
DX cooling operation
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