Low Discharge Superheat
refrigeration
Description
Compressor discharge superheat is below 68°F (20°C) after three minutes, and the unit gives alarm only.
Activation Conditions
Compressor discharge superheat is less than 68°F (20°C) after three minutes of engaging the Econ SH offset logic, the compressor is on, and Evaporator Flood back control hasn’t been active in the last three minutes and suction superheat is greater than 40°F (4.4°C) NOTE This alarm can be caused by a stuck open ECXV or LIV, causing too much liquid to be sent into the compressor at the economizer connection. An inaccurate pressure transducer or temperature sensor reading (discharge or economizer) can also cause this alarm.
Unit Behavior
Engine and Electric Operation: Alarm only.
Reset Conditions
Discharge superheat is more than 72°F (22°C), or alarm may be manually reset via keypad 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, suction and economizer pressures with those shown in Unit Data. The ECOP should read between the CSP and the CDT, if not it indicated the ECOP has failed. Refer to Section 8.9.11 for instruction on comparison. If discharge pressure is in normal range, proceed to step 5. 2. Check Suction, Discharge and Economizer Temperature Sensors a. Check economizer temperature sensor insulation integrity, make sure insulation is properly installed. Repair or replace any insulation if required. Loose or missing insulation will cause inaccurate refrigerant temperature readings. b. Inspect sensor and connectors. Verify there is no damage to sensor, and no damage, moisture, or corrosion in connectors. c. Check sensor resistance. (Refer to Note 3 in Notes Section.) 10,000 Ohms @ 77°F (25°C). Refer to Table 8–3 for chart of resistances for different sensors. 3. Check Economizer Pressure Transducer - Inspect sensor and connectors. Verify there is no damage to sensor, and no damage, moisture, or corrosion in connectors. 4. Perform Pretrip - Clear the Active Alarm list, then run a Pretrip and check for any new alarms. Any active alarms must be corrected and cleared before proceeding. 5. Check Expansion Valves, EVXV, ECXV a. Visually inspect valve. Verify there is no damage to valve, and no damage, moisture, or corrosion in coil. Check coil is seated properly. b. Check operation of valve. Refer to Section 8.9.8. 6. Check Liquid Injection Valve (LIV) - Inspect valve and coil. Verify there is no damage to valve, and no damage, moisture, or corrosion in coil. Refer Section 8.9.9