The core function of a freeze dryer is to achieve freeze-drying of materials through low-temperature condensation and vacuum environment. If the equipment fails to cool, it will directly affect production efficiency and product quality. The following is a systematic analysis and solution steps for the problem of refrigeration failure in freeze dryers, covering principle analysis, common causes, troubleshooting methods, and preventive measures.
1、 Principle of refrigeration system for freeze dryer
The refrigeration system of a freeze dryer usually consists of four major components: compressor, condenser, expansion valve (throttling device), and evaporator, which transfer heat through the circulation of refrigerants (such as R22, R404A, etc.). The workflow is as follows:
1. The compressor compresses low-temperature and low-pressure gaseous refrigerant to output high-temperature and high-pressure gas;
2. High temperature gases dissipate heat and liquefy in the condenser, releasing heat;
3. The liquid refrigerant is depressurized through an expansion valve and transformed into a low-temperature and low-pressure liquid gas mixture;
4. Low temperature refrigerant absorbs heat in the evaporator and evaporates into a gaseous state, thereby reducing the evaporator temperature (usually -40 ℃~-80 ℃) and providing a cold source for the freeze-drying box.
If the refrigeration system fails, it is necessary to investigate one by one from the aspects of refrigerant circulation, component performance, electrical control, etc.
2、 Classification of common reasons for non cooling
1. Refrigeration system malfunction
-Refrigerant leakage (the most common cause, accounting for over 60% of cases);
-Compressor damage (startup failure, winding burnout, mechanical jamming);
-Poor heat dissipation of the condenser (dust blockage, fan failure, insufficient cooling water);
-Expansion valve blockage or failure;
-Frost or ice blockage on the evaporator.
2. Electrical control issues
-Temperature controller setting error or sensor malfunction;
-The compressor starting relay is damaged;
-Power supply phase loss or unstable voltage;
-PLC program abnormality or motherboard malfunction.
3. Environmental and operational factors
-The ambient temperature is too high (over 35 ℃), and the condensation pressure is too high;
-The insulation layer of the freeze-drying box is damaged and the cooling capacity is lost;
-Operational errors (such as not turning on the cooling switch or adjusting parameters incorrectly).
3、 Troubleshooting and resolution steps
Step 1: Basic check
1. Power supply and switch status
-Confirm that the device is powered on and check if the main power switch and emergency stop button have been reset;
-Use a multimeter to measure the power supply voltage of the compressor (three-phase 380V ± 5% or single-phase 220V ± 10%).
2. Temperature controller settings
-Check if the set temperature is lower than the ambient temperature (e.g. set to -50 ℃, while the room temperature is 25 ℃);
-Restore the factory settings or calibrate the temperature sensor to eliminate display errors.
3. Compressor startup status
-Listen to the sound of the compressor: there is a brief buzzing sound during normal startup;
-Touch the surface of the compressor: there should be noticeable vibration and temperature rise during operation;
-If the compressor does not respond, check if the starting relay and thermal protector have tripped.
Step 2: Special testing of refrigeration system
1. Determination of refrigerant leakage
-Visual inspection: Observe whether there are oil stains (refrigerant and lubricating oil mixed leakage) at the copper pipe joints and valves of the evaporator and condenser;
-Pressure test: Use a manifold gauge to check the system pressure. If the low-pressure side pressure is less than 0.1MPa or the high-pressure side pressure is extremely low, it indicates a leak;
-Electronic leak detector: locate trace leakage points (such as welds and threaded connections).
2. Compressor performance verification
-Short circuit the starting capacitor of the compressor or replace the spare compressor for testing;
-Measure the resistance of the compressor winding (refer to the nameplate label for normal values), and eliminate short circuits or open circuits in the winding.
3. Inspection of condenser and expansion valve
-Clean the dust on the condenser fins and check if the cooling fan is operating normally;
-Observe the frosting situation of the expansion valve: If the valve body forms white frost, it may be due to ice blockage or adjustment failure;
-Check if the expansion valve temperature sensing bulb is tightly attached to the evaporator outlet pipeline
Step 3: Electrical and Control System Troubleshooting
1. Control board and sensors
-Check the input and output signals of the thermostat, simulate sensor signals to determine if the motherboard is normal;
-Check the PLC program parameters (such as PID adjustment values, delay start settings).
2. Compressor relay and contactor
-Use a multimeter to check the on/off status of relay contacts;
-Replace the relay of the same model to test whether the compressor can start.
Step 4: Special Scene Handling
1. The ambient temperature is too high
-Install a condenser auxiliary cooling fan or water cooling system;
-Avoid prolonged operation of equipment in high temperature environments (>35 ℃).
2. Evaporator ice blockage
-Turn off the refrigeration system and heat the evaporator to melt the ice blockage (professional operation is required to prevent pipeline deformation);
-Check if the dry filter is clogged and replace it if necessary.
4、 Preventive maintenance recommendations
1. Regular maintenance
-Clean the condenser fins quarterly and check the lubrication of the fan bearings;
-Check the refrigerant pressure annually and supplement it to the specified range (such as low pressure of 0.4~0.6MPa in R22 system).
2. Replacement cycle of key components
-Compressor lubricating oil: replace every 2 years;
-Dry filter: replace every year;
-Electromagnetic valve and expansion valve: Check and calibrate every 3 years.
3. Operating standards
-Avoid frequent starting and stopping of the compressor (interval>5 minutes);
-Strictly control the loading capacity of the freeze-drying box to prevent insufficient cooling capacity.