Freeze dryer Troubleshooting Guide Failure Detection and Elimination
Freeze-drying, also known as lyophilization, is a critical process in various industries, including pharmaceuticals, food, and biotechnology. Ensuring the proper operation of a freeze dryer is essential to avoid production delays, product loss, and equipment damage. However, freeze dryers can experience a range of operational issues that need immediate attention. This troubleshooting guide focuses on the failure detection and elimination of common freeze dryer problems. By understanding these failures and their causes, operators can maintain optimal performance and minimize downtime.
Freeze dryer troubleshooting guide of (Power Supply)
Fuse Failure (Circuit Breaker) (Power Supply): This failure appears if a fuse has been released. The cause for this failure is a short circuit.
Emergency power active: If there is a power failure, the system switches over to the emergency power supply, i.e., the freeze-drying programs are run only with the machines that are necessary to protect the product.
Emergency off active: An operator pressed an emergency off button. The power of the outputs is switched off. Check the emergency off They have to be unclamped.Push one of the control on buttons.
Main Power restored: This alarm message appears if, after a power failure, the main power was restored.
Voltage too low: Voltage of the power supply too low. This alarm message appears if the voltage control relay for the main power supply gives an alarm.
Freeze dryer Troubleshooting guide of (Operating media)
Compressed air not available (operating media): This failure appears when the pressure of the compressed air needed to operate the electro-pneumatic valves is not high enough.
Cooling water not available: This failure appears when the pressure of cooling water in the tower pipe is not sufficient.
Clean steam not available: This failure appears when the pressure of the steam in the supply line to the Freeze-Dryer is too low.
Venting gas not available:Â This failure appears when the pressure of the venting gas in the supply line to the freeze-dryer is too low.
Media not available: This failure appears when the answer of a media request to the utilities is negative.
PLC battery: This failure message appears if the voltage of the PLC battery is too low.
This failure message appears if one of the Profibus-Station fails. The causes of this failure could be:
- Internal error in the station
- no connection to the bus
- Â no power-supply at the Profibus Station.
Freeze dryer Troubleshooting guide of (SCADA)
No response from PLC 1 program: The life bit of PLC is static. The CPU of the PLC is in stop mode. And the Ethernet communication to the PLC is interrupted.
Failure Freeze Dryer PLC Communication: The Ethernet communication to the PLC is interrupted.
Freeze dryer Troubleshooting guide of the hydraulic systemÂ
Failure Hydraulic-pump: This message is given when the motor contactor for the hydraulic pump is activated, but there is no report that the pump is ON.
The causes of this failure could be:
- The corresponding motor protection switch has cut out and switched off the pump.
- The coil of the motor contactor is
The control wire to the motor contactor has been interrupted.
Failure of a hydraulic valve: This failure message appears if a hydraulic valve is too long switched on:
- A door bolt doesn’t reach the limit
- A door drive doesn’t reach the limit
- The chamber/condenser valve doesn’t reach the limit
The shelf system doesn’t reach the limit switch.
Hydraulic oil excess temperature: This failure message appears when the excess temperature safety switch has switched off the hydraulic pump. The hydraulic pump is switched on automatically again after a cooling down period. The causes of this failure could be:
The hydraulic pump was running to long.
Level hydraulic oil low: This failure message appears when the level switch LSA 2.0 reports a low level of the hydraulic oil. The causes of this failure could be:Â Leak in the hydraulic system.
Filter hydraulic polluted: This failure message appears when the differential pressure switch PDS 2.0 reports high pressure at the hydraulic oil filter. The causes of this failure could be:
The hydraulic oil filter is polluted because of dirty hydraulic oil.
Failure of a pneumatic valve: This failure message appears if a pneumatic valve is too long switched on: A door bolt doesn’t reach the limit switch.
Shelf position cannot be kept
This shelf position can not be kept Failure appears when the shelf position is not stable after reaching the shelf position. When the setshelfposition is reached, the current shelf position is stored. Alarm conditions are: The current shelf position has changed to the position that was stored for more than 5 mm, or the current shelf position has left its set position within 5 minutes after reaching the set position. Condition: No shelf movement initiated. The causes of this failure could be:
 Failure in hydraulic circuit, and Failure shelf-position measuring system
DF Alarm: venting gas nitrogen not selected
If “solvent discharge during unloading” or “product with TBA” is selected but no nitrogen for venting gas during defrosting is chosen,.
DF Alarm: Defrosting not performed after previous Freeze Drying
If defrosting after a freeze drying cycle with “solvent discharge during unloading” or “product with TBA” selected has not been finished properly, e.g., after power loss, this alarm is generated when the start of a cycle except defrosting is requested.
Freeze dryer Troubleshooting of (Door)
Door not closed:Â
This door not closed failure message appears if the report “Chamber Door Closed” has not been given. This report is a pre-condition to start the program. The causes of this failure could be:
- The chamber door is still open, or the door bolts are not in the proper position.
- The Chamber door is closed, but the “chamber closed” limit switch has not been pressed sufficiently by the chamber door.
- The chamber door is closed, but the bolts have not come
- The chamber door is closed and the bolts have come forward, but one or more bolts have not come forward sufficiently or some of the bolt limit switches have not been properly
The hydraulic pressure switch “bolts forward” has not been activated.
Freeze dryer Troubleshooting of (heating system)
Failure Silicone oil heating element:
This failure silicon oil heating element message appears when the related heating element contactor is switched on, but the status ON is not given. The causes of this failure could be:
The corresponding heating element protection switch has tripped. The coil of the corresponding heating element contactor is The control line to the heating element contactor has been interrupted.
Heat exchanger heaters excess temperature
This heat exchanger failure message appears when the excess temperature safety switch has switched off the heaters. The heaters are switched on automatically again when the silicone-oil temperature has cooled down again and because the temperature switches have automatically reset to normal status.
The causes of this failure could be:
The temperature set in the recipe is higher than the temperature set at the switches. The temperature set at the switch is too low or the switch is defective. The connecting line to the switch has been interrupted or the switch is defective. The flow in the silicone-circuit is too low
Freeze dryer Troubleshooting of (circulation pump for silicone oil)
Failure Silicone oil pump: This failure message is given when the related motor contactor is commanded on, but the status ON is not reported. The causes for this failure could be:
Motor protection switch in the power distribution cabinet has. The coil of motor contractor is. The control line to the motor contactor has been interrupted
Silicone oil pump excess temperature:
This failure message appears when the motor winding high temperature switch has switched off the pump. The pump is switched on automatically again when the temperature has cooled down again because the temperature switch has automatically reset to normal status.
The causes of this failure could be:
The connecting line to the switch has been interrupted or the switch is defective. The flow in the silicone oil circuit is too low. The excess temperature safety switch is defective
Freeze dryer Troubleshooting of a temperature element
The temperature transmitter with RTD input provides a measuring signal of 4 to 20 mA. This failure is reported when the measuring signal is not between the lower and upper limits. These are individual alarms for each temperature transmitter with RTD.
The causes of this failure could be:
The measuring loop of the converter is interrupted. The measuring loop to the RTD has been interrupted. There is a short-circuit in the measuring lead to the RTD or in the RTD itself.
There are contact resistances at the contact points of the wire connections. The analog inputs boards of the PLC or field bus stations are
The pressure transmitter provides a measuring signal of 4–20 mA. This failure is reported when the measuring signal is not between the lower and upper limits. The causes of this failure could be. The measuring transducer is The measuring loop has been interrupted
Failure Position element:
The measuring transmitter corresponding to position sensor gives a measuring signal of 4 to 20 mA. This failure is reported when the measuring signal is not between the lower and upper limits.
The causes of this failure could be:
The position sensor or the measuring transmitter is. The measuring circuit has been interrupted.
Failure Flow Meter:
The measuring transmitter corresponding to flow meter gives a measuring signal of 4 to 20 mA. This failure is reported when the measuring signal is not between the lower and upper limits.
The causes of this failure could be: The flow meter or the measuring transmitter is defective. The measuring circuit has been interrupted
Failure conductivity transmitter:
The measuring transmitter corresponding to the conductivity sensor gives a measuring signal of 4 to 20 mA. This failure is reported when the measuring signal is not between the lower and upper limits.
The causes of this failure could be: The conductivity sensor or the measuring transmitter is defective. The measuring circuit has been interrupted
Freeze dryer Troubleshooting of the cooling system
Compressor excess pressure:
This failure message appears when one of the excess pressure safety switches has cut out. The corresponding compressor has been switched off. After the failure has been eliminated, the compressor that was switched off is released and can be restarted only after an additional waiting period has elapsed.
The cause of this failure could be:The pressure in the liquefier is too high; i.e. the cooling water flow to the corresponding liquefier should be checked
Compressor oil pressure difference not ok
Refrigeration experts must be called to eliminate this failure. This failure message appears when one of the oil pressure monitoring switches has cut out.
The corresponding compressor was switched off. After the bimetallic trigger in the switch has cooled down, this failure must be acknowledged by pressing an unlocking button installed in the switch casing. This switch is located beside the compressor.
The causes of this failure could be: Lack of oil. There is too little oil in the crankcase of the corresponding compressor.Foaming of the oil through the presence of refrigerant.
Compressor excess temperature:
This failure message appears when one of the motor protection systems (monitoring of the coil temperature of the drive motors by thermistors) has cut out. The corresponding compressor was switched off.
After the failure has been eliminated, i.e. after the motor coil has cooled off, the compressor that was switched off is restarted only after an additional waiting period has elapsed.
The causes of this failure could be:Short-circuit in the coil of the. The compressor was switched on and off too often in rapid. Lack of refrigerant. Check the injection valves.
Failure Compressor:
This failure compressor message appears when the following has occurred with one of the motor protection switches installed in the power distribution cabinet for compressors:
- The motor protection switch was not switched
- The motor protection switch cut out and switched off its corresponding compressor.
The cause of failure b} could be: Short-circuit in the coil of the. The compressor was switched on and off too often in rapid succession.
Failure overheating controller:
A refrigeration expert must be called to eliminate this failure. The cooling controller unit failed. This failure message appears when one of the cooling controllers (silicone oil cooling or condenser cooling) failed. Look in the manual of the controller to get more information
Freeze dryer Troubleshooting guide Vacuum system
Failure Vacuum Pump:
Failure Vacuum Pump: This failure appears when the motor contactor is switched on but the message ON is not given. The causes of this failure could be:
One or more of the motor protection switches have cut out and switched off the corresponding vacuum pump. The coil of the corresponding motor contactor is control line to the motor contactor has been interrupted
The causes of this failure could be:
- One or more of the motor protection switches have cut out and switched off the corresponding vacuum pump.
- Failure of the vacuum pump displayed by the “SP-Guard” of monitoring system.
- Failure oil : The oil temperature has exceeded the warning limit.
- Failure level: The oil level drops below
- Failure vibration: The vibration level has exceeded the warning limit.
- Failure exhaust pressure: The exhaust pressure exceeds the maximum permissible pressure of 1200 mbar
Temperature of vacuum pump too high:
This failure appears when the temperature switch in the case of the vacuum gives a signal that the pump is too hot. The causes of this failure could be:
The support of cooling water is interrupted, and There is lack of cooling medium in the vacuum pump
Freeze dryer Troubleshooting guide of valve
 Failure valve
This report is given when the valve is activated to open but the CLOSED switch is still activated or when the valve is not activated to open but the CLOSED switch has not been activated. The causes of this failure could be:
The valve coil is defective or the plug has not been plugged on properly, Activation of the limit switch is defective. The connecting wires to the valves or to the limit switches has been interrupted. The pressure of the compressed air that activates the electro-pneumatic valves is too low.
Freeze dryer troubleshooting guide (of CIP System)
Failure CIP-pump:
This failure message is given when the related motor contactor is commanded on, but the status ON is not reported. The causes for this failure could be:
Motor protection switch in the power distribution cabinet has tripped. The coil of the motor contractor is defective. The control line to the motor contactor has been interrupted
Failure frequency inverter
This failure message is given when the related frequency inverter gives a general failure message.The detailed failure message will be shown at the frequency inverter display. Use the manual of the inverter to investigate the problem
Freeze dryer Troubleshooting guide for Water Ring Pump
FailureWRP:
This failure appears when the motor contactor is switched on, but the report ON is not given. The causes of this failure could be:
The corresponding motor protection switch has cut out and switched off the water ring pump. The coil of the corresponding motor contactor is defective. The control line to the motor contactor has been interrupted
Failure valve water supply WRP
The water supply valve is open, but the cooling water control switch does not report that there is sufficient water flow.
The causes of this failure could be: A manual shutoff valve in the line has been closed. The amount of cooling water is not enough.
Freeze dryer Troubleshooting guide of Process
FD Alarm Pressure at segment end is too high
If at the end of a pressure segment the chamber pressure remains higher than admissible for a longer time, a failure message is given. The causes of this failure could be: Failure of a too short ramping time,
Failure of the vacuum system ( leak, failure vacuum pumps) Failure of N2 pressure regulation
Shelves distance between ALUS and FD is different
This failure appears when the shelving option shelves distance in the ALUS and FD is different
Process not started:
The operator started a process. The process didn’t start, and this failure message appeared. The causes of this failure could be: A pre condition for this process is not fulfilled
FD Alarm: Chamber pressure > Pmax:
This failure appears if the pressure rise in the system is higher than the pressure P-max set in the recipe. A failure message is given in the following cases: The oil in the vacuum pumps is dirty. If at the beginning of primary drying, during the first evacuation, the pressure in the system does not fall below the set pressure plus P-max pressure value within the time set in the recipe.
If, during PRIMARY and SECONDARY DRYING and UNLOADING TEMPERATURE, the pressure in the system rises above the set P-max pressure
The causes of this failure could be:
- The door seal is defective or durable
- There is a failure in the evacuating system
- The condenser temperature is too high
- One of the valves connected to the freezer-Dryer is not tight
- There is water in the chamber or in the condenser
FD Alarm: Failure Temperature during Segment
In the freeze-drying program, an admissible temperature deviation tolerance for monitoring the ramps has been pre-set. If the temperature value remains higher or lower than this admissible deviation for a longer time without interruption, a failure message is given.
The causes of this failure could be: The steepness of a preset ascending or descending segment was chosen higher than the maximum heating rate, cooling rate, or evacuation rate of which the freeze-dryer is capable. Due to failures in the cooling or heating system, the pre-set temperature cannot be maintained.
FD Alarm: Failure Temperature at Segment end
In the recipe of the freeze-drying program, an admissible temperature deviation for the corners of the temperature ramps has been pre-set.
If at the end of a segment—i.e., at a corner—the temperature deviation is higher than the admissible value, the program is stopped until the temperature is again within the admissible limits. In the last freezing segment, the set value must have been reached (+/- 0.5’C).
If at the end of a temperature segment the temperature deviation remains higher than admissible for a longer time, a failure message is given.
The causes of this failure could be: the steepness of a preset ascending or descending segment was chosen higher than the maximum heating rate, cooling rate, or evacuation rate of which the freeze-dryer is capable. Due to failures in the cooling or heating system, the pre-set temperature cannot be maintained.
FD Alarm: Failure Condenser cooling
This failure message is given in the following case: The required minimum temperature in the condenser has not been reached within a certain pre-set time after the above-mentioned programs have been switched on. The cause of this failure could be: Failures in the condenser cooling
FD Alarm: Failure evacuation
If at the beginning of primary drying, during the first evacuation, the pressure in the system does not fall below the P-max pressure value within the time set in the recipe. The causes of this failure could be:
- The door seal is defective or dirty.
- There is a failure in the evacuating system
- The condenser temperature is too high.
- One of the valves connected to the freezer-Dryer is not tight
- There is water in the chamber or in the condenser.
CIP Alarm: Pressure CIP water is not OK.
This failure message appears due to the pressure being smaller than the set point for 30 seconds The cause of this failure could be: Failure in the CIP circuit system and failure of the pressure sensor
CIP Alarm: Temperature CIP water is not O.K.
This failure message is The temperature is not in the tolerance for 30 Seconds The cause of this failure could be: Failure in the CIP system and failure of the temperature sensor
CIP Alarm: Conductivity CIP media too low
This failure message is observed due to the conductivity being under the set point for 30 seconds, and the cause of this failure could be: Failure in the CIP system and Failure of the conductivity sensor
CIP Alarm: Timeout CIP water inlet
This type of failure message observed due to the following case:
- The unit remains longer than 1O minutes in step ”water inlet.” The cause of this failure could be:
- Failure in the GIP circuit system
- Failure of the flow meter
Process step timeout
This failure message is obsvered due to the unit remaining longer than the pre-set time in a sub-process step. There is a different hard-coded pre-set time for every sub-process step.
Cool down rate of shelves too low
This failure message is given during the unit test if the cool-down rate of the shelves is too low. Check the cooling circuits of the individual cooling compressors that cool the heat transfer fluid
Cool down rate of the condenser too low
This failure message is given during the unit test if the cool-down rate of the condenser is too low. Check the cooling circuits of the individual cooling compressors that cool the condenser
Evacuation rate too low
This failure message is given during unit testing if the pump-down rate of the unit is too low. Via Windows PC, in manual mode (all other programs are off), check the ultimate pressure of the pumps
By switching on vacuum pumps individually (by measuring point). Compare these values with the characteristic values of the pumps. To be Check the nitrogen gas flow
Heating rate of shelves too low
Check the current input or the resistance of the individual heating groups to determine whether one or more heating rods are defective.
System not Leak Tight
This type of failure message occurs while checking the system for leaks. Then precautions are to be taken during the leak test cycle start.
Check the door, Check to see whether there is water in the condenser or in the, If necessary, carry out leak detection at the Freeze-Dryer: check the flange connection, valve seats, etc.
Heating of shelves not possible
Heating of shelves is not possible. AÂ report is given when the difference between the set temperature value and the actual value is smaller than 1 oC. When this happens, the heating of the heat transfer fluid is omitted.
Evacuation not possible
This message is given if the required temperature in the condenser cooling coils is not reached within the set time.
Leak Test not possible
This message appears if in the plant test program only the LEAK TEST sub-program is switched on and the required ultimate vacuum set as the starting point for the pressure rise measurements is not reached within the set time
Bellow leaky
This message appears if during the step leak test the pressure in the bellows of the piston rod falls below the user preset minimum bellows pressure. Maintenance work Check the system for leaks.
Integrity Test Alarm: Test pressure not built up
It is not possible to build up the test pressure. The cause of this failure could be: The filter is damaged or there is no compressed air to build up the pressure available
Integrity Test Alarm: Test pressure too high
The test pressure is too high,The pressure increased to fast. The test pressure is too The cause of this failure could be: Adjustment of compressed air wrong
Integrity Test Alarm Pressure drop too high
The pressure drop is not in the tolerance. The cause of this failure could be: The filter is damaged
Water temperature in filter is not stable
The temperature difference of the water in the filter is too high for the filter test. The cause of this failure could be: The temperature in the basement is too high .The start time of the test after SIP was too short
Air temperature too low
The temperature of the air to dry the filter is too low. The cause of this failure could be: No steam available; Adjustment of steam supply for the heat exchanger wrong
Pressure deviation during drying too high
This failure appears when the pressure deviation during drying is too high. The causes of this failure could be:
- Failure of the flow controller, Failure of the vacuum system ( leak, failure vacuum pumps)
Freeze dryer Troubleshooting guide of venting system
Heater venting line excess temperature
This failure message appears when the excess temperature safety switch has switched off the heaters. The heaters are switched on automatically again when the venting gas temperature has cooled down again and because the temperature switches have automatically reset to normal status.
The causes of this failure could be that the connecting line to the switch has been interrupted or the switch is defective. The gas flow in the venting gas heater is too low
VS Alarm: Amount of H2O2 not sufficient for the process:
This failure message is given in the following case: The unit remains longer than 10 minutes in step “preparation.” The cause of this failure could be: Failure of the liquid level sensor
Deviation from the set value too high
This failure message is given in the following case: During H202, the cause of this failure could be: H202 Injection Amount per Pulse or Acceptable Injection Amount Deviation per Pulse
VS Alarm: Abort due to wet or leaky vessels
Check the system for wetness or leaks. this type of massage observed during then to be
- Check the door
- Check to see whether there is water in the condenser, in the chamber or venting filter.
- If necessary, carry out leak detection at the freezer: check the flange connection, valve seats, etc.
Gas sample pump
This message is given when the motor contactor for the gas sample pump is activated, but there is no report that the pump is ON.
The causes of this failure could be: The corresponding motor protection switch has cut out and switched off the pump. The coil of the motor contactor is defective. The control wire to the motor contactor has been interrupted.
Gas sample flow too low
Gas sample pump 9M3 switched but gas sample control switch does not report that there is sufficient gas flow. The causes of this failure could be:
A manual shutoff valve in the line has been The amount of gas sample is not enough
Below minimum vaporizer temperature
This type of failure message is obsolete due to the The cause of this failure could be: The temperature from the vaporizer is to low. Check the heaters of the vaporizer to determine whether one or more heater are defective. and , which measures the temperature of the vaporizer
Freeze dryer Troubleshooting guide of Transmitter
Temperature difference not ok:
This failure message appears if the temperature difference between the two corresponding temperature elements is too high. The cause of this failure could be: Failure in one of the temperature elements
Circuit flow is not ok.
This failure message appears if the flow in the shelf or condenser circuit is too low. The cause of this failure could be: Failure of the silicone oil pump.Frozen oil in the LN2 heat exchanger. Leak in the silicone oil circuit
Freeze dryer Troubleshooting of drive
Maintenance message:
This failure message appears if the maintenance hours counter exceeds the predefined number of operating time hours. In this case, the number of operating time hours has to be reset in the SCADA system.
Freeze dryer Troubleshooting of System of oil of silicone
Temperature of the too-low bookshelves (LN2) This message of defect appears if the temperature of the bookshelves were inferior to -65’C.
Freeze dryer Troubleshooting of PLC
Connection to ALUS failed: This failure appears when the connection between ALUS and FD is not present
Conclusion of Freeze dryer Troubleshooting Guide
Effective troubleshooting of freeze dryer systems is essential to ensure continuous, efficient operation and to protect valuable products during the freeze-drying process. By understanding the various failure types—whether related to power supply, operating media, SCADA systems, or hydraulic components—operators can take prompt corrective actions to minimize downtime and prevent costly damage. Regular maintenance, timely detection of issues, and the use of this troubleshooting guide will enhance system reliability, prolong equipment life, and maintain the quality of the freeze-dried products. A proactive approach to failure detection and elimination is key to optimizing freeze-dryer performance.