High Compressor Discharge Temperature Shutdown

Common Symptoms

• Unit shuts down mid-cycle and displays alarm code 82 on the Smart Reefer 4 (SR-4) panel
• STOP or alarm indicator light is active on the control panel
• Unit will not restart after shutdown, stays locked out until alarm is cleared
• Box temperature begins rising because refrigeration has stopped
• Compressor or refrigeration section feels extremely hot to the touch
• Unit may have been running for an extended period before the shutdown occurred
• Alarm code 82 reappears shortly after clearing and attempting a restart

Probable Causes (Ranked by Likelihood)

• Low refrigerant charge causing the compressor to run hot due to insufficient suction gas cooling Very Likely
• Refrigerant overcharge or non-condensable gases (air) in the system raising head pressure and compressor discharge temp Very Likely
• Condenser coil clogged with dirt, debris, or produce residue blocking airflow and preventing heat rejection Very Likely
• Condenser fan motor or blade not spinning at full speed or seized, reducing condenser airflow Likely
• High ambient temperature operation combined with a partially restricted condenser pushing the system over the discharge temp limit Likely
• Faulty or out-of-calibration compressor discharge temperature sensor sending a false high reading to the controller Possible
• Liquid line restriction or plugged filter-drier causing refrigerant starvation at the evaporator and elevated compression ratio Possible

Step-by-Step Diagnostic Procedure

1. Step 1. Before anything else, let the unit cool down for at least 20-30 minutes with the unit in OFF. Attempting to restart a still-hot compressor will just trigger code 82 again immediately.

2. Step 2. Navigate to the Alarm Menu on the Smart Reefer 4 (SR-4) and note any other active or stored alarm codes alongside code 82. Codes like 02 (high pressure), 10 (low refrigerant), or condenser fan fault codes often appear together and point you toward the real root cause.

3. Step 3. Inspect the condenser coil on the outside of the unit. Look for mud, insects, leaves, or produce debris packed into the fins. A clogged condenser is one of the most common reasons a unit in Central Valley summer heat trips code 82. Clean the coil with compressed air or low-pressure water from the inside out if needed.

4. Step 4. Check that the condenser fan is spinning freely and at full speed when the unit runs. With the unit in MANUAL mode, start the unit and watch the condenser fan. A slow or intermittent fan is easy to spot. If the blade is cracked or the motor is dragging, replace the fan motor or blade before going further.

5. Step 5. Check refrigerant pressures with a manifold gauge set. Low suction pressure combined with high discharge pressure points to a refrigerant charge problem (undercharge or restriction). High suction and high discharge together suggest overcharge or non-condensables. If you are not certified to work with refrigerants, stop here and call a refrigeration tech.

6. Step 6. Locate the compressor discharge temperature sensor, typically mounted on the compressor discharge line near the compressor head. Inspect the sensor wiring harness and connector for corrosion, chafing, or backed-out pins. A damaged sensor can send a false high signal and cause a phantom code 82 even when the compressor is not truly overheating.

7. Step 7. If the sensor wiring looks good and you have a multimeter, check sensor resistance at ambient temperature and compare to the Thermo King temperature-resistance chart for the sensor type on your unit. A reading far outside the expected range at a known temperature confirms a bad sensor.

8. Step 8. If the condenser is clean, the fan is good, and the sensor checks out, the refrigerant system likely has a charge or restriction issue. A refrigeration-certified tech with recovery equipment and a vacuum pump will need to recover the charge, replace the filter-drier, check for restrictions, and recharge to spec. This step requires specialty tools and EPA certification.

Frequently Asked Questions