High Discharge Pressure
refrigeration
Description
The compressor discharge pressure switch opens as discharge pressure rises; engine operation shuts down the engine and unit and alarms, and electric operation shuts down refrigeration and alarms with PSCON still energized.
Activation Conditions
Compressor discharge pressure switch (HPS) contacts are open. HPS contacts open when the discharge pressure rises. Refer to Section 2.9.
Unit Behavior
Engine Operation: Engine and unit shutdown and alarm. Electric Operation: Refrigeration system shutdown and alarm with PSCON still energized. CSMV at 50% and EVXV controls superheat.
Reset Conditions
Auto reset after 15 minutes if the compressor discharge pressure falls below limit, 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 System Pressures - Install manifold gauge set and check and compare compressor discharge and suction pressures with those shown in Unit Data. Refer to Section 8.9.11 for instruction on comparison. If discharge pressure is in normal range, proceed to step 5. 2. Check Airflow Through Radiator and Condenser Coil a. Inspect condenser and radiator. Ninety percent or more of the coil surface must be undamaged. Condenser/Radiator coil must be clean. b. Check airflow (with unit running). Verify even airflow through the entire coil, and no “dead” spots. c. Check condenser fan rotation / operation. Fans should operate correctly. Air should be directed in through the grill, and into the engine compartment. 3. Perform Pretrip - Check CSMV and ECXV tests. Refer to Section 3.7. Pass Test. 4. Check Refrigerant Charge - Refer to Section 8.7.2. Charge must be correct. 5. Check HPS Power And Wiring a. Inspect switch, connector pins and terminals. Verify that there is no physical damage to the switch. Check the connections for damage and corrosion. b. Check for power from 1-2MSM-16 to PM-22. If a minimum of 11 VDC is not present, check connectors and wiring between terminals for damage, moisture or corrosion. c. Check continuity from HPS-B to PM-22 and HPS-A to OGF-S+. If both are good, replace HPS. If good continuity is not present, check connectors and wiring between terminals for damage, moisture or corrosion. 6. Check HPS a. With discharge pressure below the switch closing pressure (refer to Section 2.9), check continuity from HPS-A to PM-22. If there is no continuity replace the switch. b. Check switch operation. Test switch. Refer to Section 8.9.10 step b. 7. Refer to Refrigeration Troubleshooting - Refer to Section 6.4. Discharge must be in range for the current ambient and refrigerated compartment conditions.