Low Discharge Pressure
refrigeration
Description
In Pretrip heat, compressor discharge pressure did not rise to normal, and Pretrip will abort and display “PRETRIP FAILED IN TEST 4” in MessageCenter.
Activation Conditions
In Pretrip heat, the compressor discharge pressure did not rise to normal. (“Normal” discharge pressure for systems operating in Pretrip heat can be estimated by adding 80 psig (5.5 bars) toe the saturation temperature of the air entering the condenser (ATS reading).
Unit Behavior
Pretrip will abort and “PRETRIP FAILED IN TEST 4” will be displayed in MessageCenter.
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 Wiring to CDP and CSP a. Verify that correct wires are connected to each transducer. Plugs to transducers are the same. The correct wire plug must be connected to the proper transducer. The CDP connector is identified with a red tape band while the CSP connector is identified with a blue band. b. Verify that correct transducer is installed in each position. Mechanical connections are the same. The CDT should have a red dot on it while the CST has a blue dot. 2. Check for Alarms a. Check for 00121 Check Ambient Air Sensor or P00158 Check Ambient Air Sensor. Alarm conditions must be corrected and the alarm cleared to continue. b. Check Ambient Sensor reading. Must be within ±10°F (±5.5°C) of actual temperature. 3. Check System Pressures a. Install manifold gauge set and check and compare compressor discharge and suction pressures with those shown in Unit Data. Refer to Section 1.9.12 for instruction on comparison. b. Check transducer operation. Refer to Section 1.9.12. 4. Check Refrigerant Charge: Refer to Section 1.7.2. 5. Check SV1: Refer to SV1 Checkout Procedure in Section 1.9.5. 6. Check Compressor a. Check the operation of the high side of the compressor by covering the condenser inlet air. Discharge pressure must rise a minimum of 50 to 100 psig (3.4 to 6.9 bars). b. Remove compressor heads and inspect condition of cylinder suction valves, cylinder discharge valves and gaskets. Must be in good condition. Refer to Section 1.8.