Thermo King SR-2 SmartReefer2, Diagnostic Manual

Page: 378 / 431

Section 6 – SR-2 Service Procedure D01A
Control and Display Return Air Sensors
These sensors monitor the temperature of the air returning to the evaporator coil. The sensors are located in the
return air flow and are connected directly to the microprocessor connector J3. These sensors are graded sensors
and must be replaced with graded sensors. The microprocessor must be calibrated to the respective grade of the
installed sensor in order to operate properly. The Control Return Air Sensor is marked with one yellow cable tie
and is connected to the microprocessor via the RTP and RTN wires. The Display Return Air Sensor is marked
with two yellow cable ties and is connected to the microprocessor via the RTRP and RTRN wires. When
replacing a sensor, be certain the sensors are connected properly.
Control and Display Discharge Air Sensors
These sensors monitor the temperature of the air leaving the evaporator coil. The sensors are located in the
evaporator discharge air path and are connected directly to the microprocessor via connector J3. These sensors
are graded sensors and must be replaced with graded sensors. The microprocessor must be calibrated to the
respective grade of the installed sensor, in order to operate properly. The Control Discharge Air Sensor is
marked with one red cable tie and is connected to the microprocessor via the DTP and DTN wires. The Display
Discharge Air Sensor is marked with two red cable ties and is connected to the microprocessor via the DTRP and
DTRN wires. When replacing a sensor, be certain the sensors are connected properly.
Hard and Soft Failures
Sensor alarms can occur in the following ways.
A “Hard Failure” is defined by an out of range sensor reading, typically caused by an open or shorted sensor.
The sensor display will show dashes if a hard failure occurs. If this occurs only the alarm code for that sensor will
be set. Alarm code 13 will not be present. The controller may not be showing dashes for the sensor reading, but
the alarm will be active when the unit is inspected. If a sensor alarm code is set, a failure did occur at some point.
Checking a ServiceWatch data logger download at Technician Level may indicate when the hard failure occurred.
A “Soft Failure” is defined by erratic operation or sensor drift that exceeds acceptable tolerances, (sensor is out
of calibration). If this occurs the alarm code for the suspect sensor or sensors will be set along with Alarm Code
13. This indicates a potential problem that may not be immediately apparent, and that a hard failure as defined
above did not occur. Checking a ServiceWatch data logger download at Technician Level may indicate when
the soft failure occurred.
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P41RD01A 01 February 2005