Check Defrost Term 1 Sensor
refrigeration
Description
Defrost Termination Temperature Sensor is out of -53° to +158°F (-47° to +70° C.), and the unit alarms and may initiate defrost.
Activation Conditions
Defrost Termination Temperature Sensor (1DTT) is not within the range of -53° to +158°F (-47° to +70° C.)
Unit Behavior
Engine and Electric Operation: If Alarm 00022 Low Suction Superheat is not active: Alarm and initiate defrost if 1RAT is below 45°F (7.2°C). If Alarm 00022 Low Suction Superheat is also active: Alarm and initiate defrost if 1SAT is below 45°F (7.2°C). Under both of the above conditions, defrost will end after 10 minutes. If Alarms 00022 Low Suction Superheat and 00123 Check Supply Air Sensor are also both active: alarm and defrost will not be allowed.
Reset Conditions
Auto Reset when 1DTT is in range or, alarm may be manually reset via keypad or by turning the unit off, then back on again.
Corrective Actions
1. Check Sensor a. Inspect sensor and 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 8–1 for chart of resistances for different sensors. 2. Check Sensor Wiring a. Inspect harness and control box connector pins and terminals (See wiring schematic Section 10.3). Verify there is no physical damage to harness, and no damage, moisture, or corrosion in connectors. b. Power up the microprocessor (Refer to Note 2 in Notes Section). Disconnect sensor from harness. Check for Voltage 3.0 ± 0.1 VDC volts at harness plug between pins. This verifies microprocessor output and wiring connections to the sensor.