Section 5 – SR-2 Diagnostics
203 CHECK DISPLAY RETURN AIR SENSOR
Page 1 of 2
Alarm Type
Check Alarm
(Shutdown Alarm during a Pretrip Test).
Associated Alarm
Codes
Alarm Code 03 Check Control Return Air Sensor
Alarm Code 11 Unit Controlling on Alternate Sensor
Alarm Code 13 Sensor Check
Alarm Code 92 Sensor Grades Not Set
Component Description and Location
This sensor is one of two dual return air sensors. Both return air sensors must agree within specified limits. The
sensor associated with Alarm Code 203 Check Display Return Air Sensor is used for temperature display by the
HMI control panel. The sensor is located next to the control return air sensor in the return air stream. It is a graded
sensor.
Circuit Description
The display return air temperature sensor circuit is a two wire circuit. The RTRP-01 (+) wire connects the
microprocessor 35 pin sensor connector J3 pin 21 to the blue sensor wire. The RTRN-01 (-) wire connects the
microprocessor 35 pin sensor connector J3 pin 32 to the brown sensor wire. The sensor wires are routed in the
Sensor Harness. The sensor is hard wired to the sensor harness.
Considerations
1. If the unit is controlling on return air temperature, and a problem occurs with either return air sensor, the
unit will switch to Discharge Air Control and Alarm Code 11 Unit Controlling on Alternate Sensor will be set.
2. Sensor codes must be cleared from the Maintenance Menu before Alarm Code 11 will clear.
3. Sensor grades must be correctly set to the actual grade of the sensor installed. Failure to do so may result
in nuisance alarm codes.
4. Sensors should be positioned to minimize the potential for moisture entry where the wires enter the sensor
shell. Wherever possible, mount sensors with the barrel up and the wires down.
How Alarm is Set
1. The sensor is over or under range for a specified time interval. The sensor reading may return to normal.
Only Alarm Code 203 Check Display Return Air Sensor is set.
2. The sensor reading is erratic over time but did not go over or under range. Both Alarm Code 203 Check
Display Return Air Sensor and Alarm Code 13 Sensor Check are set. This indicates the sensor was
inaccurate but was not over or under range.
3. The sensor grade is set to 5H.
Both Alarm Code 203 Check Display Return Air Sensor and Alarm Code 92
Sensor Grades Not Set are set.
4. The temperatures of the control return air sensor and display return air sensor are not within a specified
range.
Alarm Code 03 Check (Control) Return Air Sensor, 203 Check Display Return Air Sensor and 13
Sensor Check are set if the faulty sensor cannot be determined. If the faulty sensor can be determined,
only the alarm code for that sensor and Alarm Code 13 will be set.
5-80
02 February 2005
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