Low Suction Superheat
refrigeration
Description
Compressor suction superheat is less than 8°F (4.4°C) for more than 3-4 minutes; engine operation shuts down the engine and unit with an alarm, and electric operation shuts refrigeration with PSCON energized.
Activation Conditions
“Check Suction Temperature Sensor” and/or “Check Evaporator Temperature Sensor” alarms are not active (refer to Alarm 000127 and/or 000131 first) and: Compressor suction superheat (Compressor Suction Temperature (CST) minus saturated temperature for Compressor Suction Pressure (CSP) is less than 8°F (4.4°C) for more than 3-4 minutes.
Unit Behavior
Engine Operation: Engine and unit shutdown and alarm. Electric Operation: Refrigeration system shutdown and alarm with PSCON still energized.
Reset Conditions
Auto reset after 15 minutes, 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 a. Check Suction and Evaporator Pressure reading at the compressor. While the compressor is running and the SMV is greater than 70% open, verify evaporator and suction pressure readings within 3 psi of each other, with evaporator pressure slightly higher than suction pressure. If not, check the Pressure Transducers. Refer to Section 8.9.11. b. Install manifold gage set and check and compare compressor discharge, suction and evaporator outlet pressure to the Unit Data readings. Refer to Section 8.9.11 for instruction on comparison. 2. Check Evaporator Section - Check evaporator section, return air bulkhead, air chute, and the evaporator coil (for cleanliness and airflow). Refer to Section 8.4.10 3. Check Suction and Evaporator Temperature Sensors a. Check Evaporator and Suction temperature sensor insulation integrity, and 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 connector. Verify there is no damage to sensor. Verify there is no damage, moisture, or corrosion in connector. c. Check sensor resistance (Refer to Note 3 in Notes Section.) 10,000 Ohms @ 77°F (25°C.) See Table 8–3 for complete table of temperatures and resistance values. 4. Check Expansion Valve (EVXV) a. Visually inspect valve. Check that the coil is seated properly. b. Check operation of valve. Refer to Section 8.9.8. 5. Perform Pretrip Check - 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.