1、 Common faults and solutions

1. Uneven temperature shock

• Fault manifestationThe temperature difference between different areas inside the box exceeds ± 2 ℃, which affects the consistency of the test.
• Possible reasons：
  • Dust accumulation or blockage of debris in the air duct can cause poor airflow circulation.
  • The fan impeller is worn or the belt is loose, and the speed is insufficient.
  • Abnormal switching of cold and hot air doors, uneven mixing of cold and hot airflow.
• maintenance measures：
  • Remove the air duct baffle, clean the dust and foreign objects with compressed air.
  • Check the tension of the fan belt and replace it if it is severely worn; The dust accumulation on the impeller needs to be cleaned with neutral detergent.
  • Debug the air door drive motor, check if the solenoid valve is stuck, and replace the seal if necessary.

2. Slow or insufficient temperature rise in the high temperature section

• Fault manifestationWhen setting a high temperature (such as 150 ℃), the heating rate is lower than 0.5 ℃/min or cannot reach the set value.
• Possible reasons：
  • Scaling on the surface of the heating tube or partial melting of the resistance wire results in a decrease in heating power.
  • Solid state relay contacts oxidize, resulting in insufficient current output.
  • Temperature control instrument parameters drift and PID adjustment abnormality.
• maintenance measures：
  • After cutting off the power, disassemble the heating tube, use sandpaper to polish the surface scale, measure the resistance value, and replace the damaged heating tube as a whole.
  • Replace the solid-state relay or wipe the contact oxide layer with alcohol.
  • Re calibrate the temperature control instrument and input the default PID parameters provided by the manufacturer (such as P=15%, I=30s, D=10s).

3. Poor cooling effect in the low-temperature section

• Fault manifestationThe arrival time of low temperature (such as -40 ℃) exceeds the rated value, or the temperature fluctuates greatly.
• Possible reasons：
  • Refrigerant leakage (common at copper pipe welds) and insufficient system pressure.
  • Poor heat dissipation of the condenser, dust accumulation on the fins, or fan shutdown.
  • The dry filter is clogged, resulting in restricted refrigerant flow.
• maintenance measures：
  • Use a halogen leak detector to detect leaks, vacuum after welding, and fill with refrigerant such as R404A according to the manufacturer's specified amount.
  • Clean the dust on the condenser fins with a brush every week, check if the fan capacitor is faulty, and replace damaged parts.
  • Replace the dry filter and, if necessary, also replace the expansion valve.

4. Abnormal control system

• Fault manifestationTouch screen displays garbled code, program interruption or alarm codes (such as E01, E03).
• Possible reasons：
  • The power supply voltage fluctuates by more than ± 10%, causing damage to the control board components.
  • The wiring of the temperature sensor (PT100) is loose or the probe is damp and malfunctioning.
  • PLC program errors are often caused by misoperation or electromagnetic interference.
• maintenance measures：
  • Configure a voltage regulator, check the fuses and capacitors on the control board, and replace burnt out components.
  • Re weld the sensor wiring, seal the probe with silicone or replace it with a new sensor when it becomes damp.
  • Contact the manufacturer's technical personnel to remotely refresh the PLC program, or install anti-interference magnetic rings in the control box.

2、 Systematic maintenance plan

1. Daily operation and maintenance

• Daily check：
  • Observe the operating current of the compressor (normal range 10-15A) and the pressure on the high and low pressure gauges (high pressure 1.2-1.8MPa, low pressure 0.2-0.4MPa).
  • Wipe the outer wall of the box and the glass observation window to avoid residual corrosive gases.
• Weekly maintenance：
  • Use a soft cloth dipped in neutral detergent to wipe the inner chamber of the box and remove any residual condensed water or volatile substances from the test sample.
  • Check the sealing performance of the door seal, and replace it promptly if it ages or deforms to prevent loss of cooling capacity.

2. Periodic deep maintenance

• Monthly projects：
  • Clean the cooling fan grille of the refrigeration system and use compressed air to blow away dust inside the control box.
  • Calibrate temperature uniformity: Place 3 standard thermometers and compare the displayed values after running the temperature cycle. If the deviation exceeds ± 1 ℃, it needs to be adjusted.
• Quarterly projects：
  • Check the tightness of the heating tube wiring terminals and apply thermal conductive silicone grease to prevent poor contact.
  • Add high-temperature resistant lubricating grease (such as molybdenum disulfide grease) to rotating components such as fans and air door drive motors.

3. Long term shutdown protection

• If the suspension exceeds 15 days, you need to:
  • Drain the accumulated water in the box and open the box door for ventilation for 24 hours to prevent mold growth.
  • Disconnect the main power supply, place moisture-proof agent inside the control box, and cover the equipment with a dust cover.
  • Power on once a month (no-load) for 2 hours each time to maintain the flow of compressor lubricating oil.

3、 Maintenance precautions

• Before maintenance, the power must be cut off, and protective gloves should be worn during refrigeration system maintenance to avoid refrigerant frostbite.
• Non professionals are prohibited from disassembling high-pressure components such as heating tubes and compressors. Operations involving refrigerants must be completed by certified personnel.
• Establish equipment maintenance records, including fault handling time, component replacement models, and calibration data, to facilitate traceability of equipment performance changes.