Low Refrigerant Pressure
refrigeration
Description
Suction pressure has been less than -6.3 psig (-0.43 bar) for the configured time or 10 seconds; engine operation shuts down the engine and unit with an alarm, and electric operation gives alarm only or shuts refrigeration if configured.
Activation Conditions
Suction Pressure has been less than -6.3 psig (-0.43 bar) for the Low Suction Pressure Configuration time or 10 seconds (whichever is less).
Unit Behavior
Engine Operation: Engine and unit shutdown and alarm. Electric Operation: Alarm only or (if configured for shutdown) refrigeration system shutdown and alarm with PSCON still energized.
Reset Conditions
Auto Reset when suction pressure rises above 0.0 (bar or psig). Alarm may be manually reset via keypad or by turning the unit OFF, then ON again.
Corrective Actions
1. Visually Inspect Unit - Visually inspect unit for damage to liquid line causing restriction or signs of temperature drop at the filter drier. All tubing from the receiver to the evaporator section must be in good condition. Verify that there is no temperature drop at the drier or anywhere on the liquid line. 2. Perform Pretrip Check - Clear the Active Alarm list, then run a Pretrip and check for alarms. Any active alarms must be corrected and cleared before proceeding. 3. Check For Low Refrigerant Charge - Check refrigerant level in the receiver. Refer to Section 8.7.2. Generally, the level should be between the upper and lower sight glasses with a refrigerated compartment temperature of 35°F (1.0°C) or lower. 4. Manually Defrost Unit - Defrost unit and terminate automatically. Typical defrost cycle time is 5-20 minutes. Suction pressure should rise gradually during cycle. 5. Check Evaporator Section - Check evaporator section, return air bulkhead, air chute, and evaporator coil for cleanliness and airflow. Refer to Section 8.4.10 6. Check System Pressures - Install Manifold Test Set and check and compare compressor discharge and suction pressures with those shown on the microprocessor. Suction pressure must be above 0.0 (psig or bar) Suction and Discharge Pressures must have the same reading on gauges and on microprocessor display. 7. Check Transducer Wiring. Refer to Section 8.9.11 a. Inspect transducer and connector pins and terminals. (See wiring schematic Section 8.) Verify that there is no physical damage to sensor, and the pins in plug are not damaged or corroded. b. Check for voltage at the transducer plug between pins A (+) and B (ground). Voltage should be approximately 12VDC. c. Reconnect the transducer plug. Check for voltage between pin C and ground. Voltage should be greater than 0.24 VDC and less than 5 VDC. 8. Check Compressor Suction Modulation Valve (CSMV) - Check CSMV. Refer to Section 8.9.7. 9. Check Expansion Valve (EVXV) - Refer to Section 8.9.8.