Return Air Sensors RAT and RAT2 Out-of-Range
electrical
Description
Return Air Sensors RAT and RAT2 Out-of-Range means RAT and RAT2 differ by more than 3.6°F (2°C) for 10 consecutive minutes or 25 out of 30 minutes; if selected, switch to SAT sensor.
Activation Conditions
RAT2 is installed and configured. RAT and RAT2 show different air temperature readings of greater than 3.6°F (2° C) for 10 consecutive minutes, or 25 out of 30 minutes.
Unit Behavior
If RAT or RAT2 is selected as control sensor, switch to SAT sensor.
Reset Conditions
Auto reset when sensor is in range or, alarm may be manually reset using the display mounted keys or by turning the unit off, then back on again.
Corrective Actions
1. Check RAT and RAT2 Sensors a. Inspect sensors and connectors. Verify that there is no damage to sensor, and no damage, moisture or corrosion in connectors. b. Check sensor resistance. (Refer to Note 3 in Section 7.2) 10,000 Ohms @ 77°F (25°C). Refer to Section 8.9.16 for chart of resistances for different sensors. 2. Check Sensor Wiring a. Inspect connector pins and terminals at sensor connector 1-3MSM (see wiring schematic). Verify that there is no physical damage to harness, and no damage, moisture or corrosion in connectors. b. Place system in PC mode. Refer to Note 2 in Section 7.2. Disconnect sensor from harness. Check for 3.0 ± 0.1 VDC at harness plug between pins. Voltage should be 3.0 ± 0.1 VDC volts at harness plug between pins. This verifies microprocessor output and wiring connections to the sensor.