7–77 62-11785
07008 CHECK REDUNDANT RETURN AIR SENSOR (RAT2)
• ACTIVATION: A Redundant Return Air Temperature Sensor (RAT2) is installed, configure, and is not within
the range of -53 to +158°F (-47 to +70° C).
• UNIT CONTROL: If RAT2 is selected as the active probe, switch active probe to RAT probe.
• RESET CONDITION: 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.
NOTE: Follow the steps below until a problem is found. Once a repair or correction has been made, the active
alarm should clear itself (refer to reset condition above). Operate the unit through the appropriate modes to see
if any active alarm occurs. Continue with the steps below as necessary.
1. Check Sensor
a. Inspect sensor & connectors. Verify there is no damage to sensor, and no damage, moisture, or
corrosion in connectors.
b. Check sensor resistance. (Refer to Note 3 in
Notes
Section) 10,000 Ohms @ 77°F (25°C). Refer to
Table 8–3
for chart of resistances for different sensors.
2. Check Sensor Wiring
a. Inspect connector pins & terminals at sensor connector 2MM. (See wiring schematic
Section 10.3
)
Verify there is no physical damage to harness, and no damage, moisture, or corrosion in connectors.
b. Place the system in PC Mode. Refer to Note 2 in
Notes
Section 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.
07009 RETURN AIR SENSORS OUT OF RANGE (RAT & RAT2)
• ACTIVATION: A Redundant Return Air Temperature Sensor (RAT2) is installed, configure, and is not
reading with (2° C).
• UNIT CONTROL: If RAT2 is selected as the active probe, switch active probe to RAT probe.
• RESET CONDITION: 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.
NOTE: Follow the steps below until a problem is found. Once a repair or correction has been made, the active
alarm should clear itself (refer to reset condition above). Operate the unit through the appropriate modes to see
if any active alarm occurs. Continue with the steps below as necessary.
1. Check Sensor
a. Inspect sensor & connectors. Verify there is no damage to sensor, and no damage, moisture, or
corrosion in connectors.
b. Check sensor resistance. (Refer to Note 3 in
Notes
Section) 10,000 Ohms @ 77°F (25°C). Refer to
Table 8–3
for chart of resistances for different sensors.
2. Check Sensor Wiring
a. Inspect connector pins & terminals at sensor connector 2MM. (See wiring schematic
Section 10.3
)
Verify there is no physical damage to harness, and no damage, moisture, or corrosion in connectors.
b. Place the system in PC Mode. Refer to Note 2 in
Notes
Section 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.
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