Low Suction Pressure
refrigeration
Description
Suction pressure is below -10inHg (-0.34 bar) for more than 30 continuous seconds or below -16inHg (-0.54 bar) for more than five seconds during Pretrip, and Pretrip will abort and display “PRETRIP FAILED IN TEST X”.
Activation Conditions
Suction Pressure is less than -10inHg (-0.34 bar) for more than 30 continuous seconds, or less than -16inHg (-0.54 bar) for more than five seconds at any time during Pretrip.
Unit Behavior
Pretrip will abort and “PRETRIP FAILED IN TEST X” will be displayed in MessageCenter indicating in which test the suction pressure was too low.
Reset Conditions
Auto reset if Pretrip is started again, 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 Fan Belts: Check upper and lower fan belt tension and condition. Verify no glazing, no cracking, no slipping. Refer to Section 1.6. Replace if required. 2. Check System Pressures: Install manifold gauge set to check and compare actual compressor discharge and suction pressures with those shown in Unit Data. Refer to Section 1.9.12 for instruction on comparison. 3. Manually Defrost Unit: Defrost unit and terminate automatically. Typical defrost cycle time is 5-20 minutes. Suction pressure should rise gradually during cycle. 4. 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. 5. Check Refrigerant Charge: Refer to Section 1.7.2. 6. Check Expansion Valve (EVXV) a. Visually inspect valve. Check that coil is seated properly. b. Check valve. Refer to Section 1.9.9. 7. Check CSMV: Check compressor suction modulation valve. Refer to Section 1.9.8.