Low Refrigerant Pressure
refrigeration
Description
Low refrigerant pressure means suction pressure is below the listed limit for the configured delay, and the unit alarms only or shuts down and alarms if configured.
Activation Conditions
The compressor is operating with the suction pressure less than -3 psig (-0.20 bar) for more than the LP SHUTDOWN DELAY Configuration (up to five minutes) with RAT above -10°F (-23.3°C) or less than -8 psig (-0.53 bar) with RAT at any temperature.
Unit Behavior
Alarm only or (if configured for shutdown) shutdown and alarm.
Reset Conditions
Auto reset after 15 minutes if suction pressure is more than -2 psig (-0.13 bar) or alarm may be manually reset using the display mounted keys or by turning the unit OFF, then ON again.
Corrective Actions
1. Visually Inspect Unit: Look for damage to the liquid line causing a restriction or any signs of temperature drop at the filter drier. Verify all tubing from the receiver to the evaporator section is in good condition. Verify there is no temperature drop at the filter drier or anywhere on the liquid line. 2. Check Airflow Through Evaporator Coil/Section a. Inspect coil. Ninety percent or more of the coil surface must be undamaged. Coil must be clean. b. Check airflow (with unit running). Even airflow through the entire coil. No “dead” spots. c. Check return air bulkhead, air chute. Good air flow. Return air not restricted. Air chute in good condition. d. Check fan clutch. Must be fully engaged. e. Check upper and lower fan belt tension and condition. Verify no glazing, cracking, or slipping. Refer to Section 1.6. Replace if required. 3. Check Refrigerant Charge: Refer to Section 1.7.2. 4. Check System Pressures: Install manifold gauge set and check and compare compressor discharge, suction and evaporator outlet pressure to the Unit Data readings. Suction pressure must be above -3 psig (-0.2 bar). Refer to Section 1.9.12 for instruction on comparison. 5. Manually Defrost Unit: Defrost unit and terminate automatically. Typical defrost cycle time is 5-20 minutes. Visually verify that all ice is cleared from evaporator coil. 6. Perform Pretrip Check: Clear Active Alarm list, then run Pretrip and check for any new alarms. Any active alarms must be corrected and cleared before proceeding. 7. Check Unloader Operation: Check Front (UL1) and Rear (UL2) Unloaders. Refer to alarm 00085 Check UL1 Circuit and 00086 Check UL2 Circuit. 8. Check Compressor Suction Modulation Valve (CSMV): Refer to Section 1.9.8. 9. Check Expansion Valve (EVXV): Refer to Section 1.9.9.