Thermo King Super II SR+, Manual, Page: 60 / 145

Electrical Maintenance (Rev 6/98)
50
The voltage drop across the sensor should be 2.3-3.4 Vdc.
The voltage drop across the sensor is directly proportional
to the sensor temperature. At a sensor temperature of
approximately 21° C (70° F), the voltage drop should be
approximately 2.95 Vdc. At a sensor temperature of approx-
imately 0° C (32° F), the voltage drop should be approxi-
mately 2.73 Vdc. The voltage drop across a sensor may vary
up to 5 percent from these examples. Voltage drops out of
this range indicate a failed sensor.
Sensor Replacement
1. Remove the old sensor from the clamp or mesh tube
that holds it in position.
2. Disconnect the old sensor from the sensor harness.
3. Connect the new sensor to the sensor harness.
4. Place the new sensor in the clamp or mesh tube from
which the old sensor was removed.
NOTE: Steps 5 and 6 must also be performed when replac-
ing return or discharge air sensors.
5. Calibrate the sensor (see Guarded Access).
6. Remark the sensor grade decal (located on the control
box) with the new sensor grade.
Return Air Sensor
Access the return air sensor by opening the right side door
and removing the lower access cover. The return air sensor
is connected to the sensor harness with a 3 pin connector at
the RTP and RTN wires.
NOTE: If the return air sensor is replaced, the micropro-
cessor must be programmed to match the grade of the new
sensor being installed. The grade number is stamped on
the new sensor. Refer to Guarded Access for calibration
procedures. The sensor grade decal on the control box
must also be remarked with the new return air sensor
grade.
Discharge Air Sensor
Access the discharge air sensor by opening the right side
door and removing the upper access cover. The discharge
air sensor is connected to the sensor harness with a 3 pin
connector at the DTP and DTN wires.
NOTE: If the discharge air sensor is replaced, the micro-
processor must be programmed to match the grade of the
new sensor being installed. The grade number is stamped
on the new sensor. Refer to Guarded Access for calibra-
tion procedures. The sensor grade decal on the control box
must also be remarked with the new return air sensor
grade.
Coil Temperature Sensor
Access the coil temperature by opening the right side door
and removing the upper access cover. The coil temperature
sensor is connected to the sensor harness with the 2 pin con-
nector at the CTP and CTN wires.
Ambient Air Sensor
Access the ambient air sensor by opening the right side
door. The ambient air sensor is located in a hole in the frame
in front of the expansion tank. The ambient air sensor is
connected to the sensor harness with a 2 pin connector at the
ATP and ATN wires.