Low Discharge Pressure
refrigeration
Description
The compressor discharge pressure is under 200 psi with the switch open for 3 seconds and AAT over 45°, and the unit alarms.
Activation Conditions
Compressor discharge pressure switch is open and discharge pressure is <200 psi and AAT >45°. Pressure must be low for three seconds consecutively.
Unit Behavior
Compressor only: If activated while compressor is off, Alarm Condition only.
Reset Conditions
Compressor high discharge pressure switch closed and Power Switch is ON OR Alarm Reset OR Cycle Power
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 AAT Sensor Reading a. Check the ambient air temperature (outside) reading on the Aspen Interface or in the system values menu in CabinTech. b. If the AAT sensor reading is higher than actual ambient temperature and ambient temperature is below 45F, the alarm may become active. Verify that AAT is not reading higher than actual due to sunlight, exhaust, or another heat source. c. Check sensor resistance. Verify that the resistance is correct for the ambient temperature. Measure resistance between J8-1 and J8-2. 3. Check Refrigerant Charge - Refer to Section 8.7.2. Charge must be correct. 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 continuity from the CCM J1-6 to HPS-B and J1-12 to HPS-A. If they are OK 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 above minimum and below maximum switch op en in g pressure (refer to Section 2.10). Check continuity between the A and B position of the switch connector. Switch should be closed. b. Check switch operation. Test switch. 7. Refer to A/C Troubleshooting - Discharge must be in range for the current ambient and cab conditions.