Freeze dryers are one of the most effective dehydration devices on the planet. They manipulate temperature and pressure to rapidly dehydrate foods, surgical transplants and more without damaging them. This process allows the freeze-dried items to last longer, extending the viability of transplants and the time that food can be stored. As a result, freeze dryers are used by restaurants, hospitals and laboratories across the world.
However, freeze dryers are susceptible to malfunction and deteriorated performance over time. They may begin to run too warm, or their vacuum pumps may begin to leak. Consistent maintenance can prevent and resolve these problems, ensuring that your freeze dryer is up and running when it is needed most.
Below are the best freeze dryer troubleshooting tips to keep your machine running longer.
First Steps Following Freeze Dryer Malfunction
When something seems wrong with your freeze dryer, there are steps to take first to assess and minimize potential damage:
- Check the basics: The freeze dryer should be plugged in, and the power switch should be set to “On.” The circuit breaker should also be operating normally.
- Soft reset the freeze dryer's controller: This step is relatively simple. The controller may be experiencing some minor software glitches that are leading to inaccurate readings or an unresponsive system. Turning the controller off and allowing it to sit for about 30 seconds before turning it back on can reset these glitches and restore the software to normal.
- Assess the condenser frost patterns: Over time, the freeze dryer condenser will develop a layer of frost across its coils. If all is operating as it should, this layer will be evenly distributed across the coils. An uneven frost pattern may be a sign that there is a vacuum leak or refrigerant issue. The same is true if frost only appears on the top condenser coils.
- Inspect the freezer's seals and gaskets: Door gaskets are susceptible to cracks and compression fatigue, which can weaken the freeze dryer and cause it to work harder to reach the same temperatures. Drain plug seals may also grow loose or cracked over time. In some cases, it may be necessary to replace them entirely.
- Examine the drain valve and line: The drain valve may become loose over time, which can lead to leaks and a weaker vacuum pump overall. Leaks are often caused by tears and cracks in the drain line. You can spot leaks like these by looking for puddles beneath the freeze dryer.
- Clean out clogged air filters: The air filter's job is to protect the freeze dryer from dust and other contaminants. In doing so, it may become clogged. Be sure to clean it out periodically to keep the dryer from overheating.
Step-by-Step Diagnostics for Leaks and Other Issues
Once you've run through the basics, it's time to narrow down the problem through a thorough diagnostic process. This process will take some time, but it will be worth it in the end, as it will let you know what the issue isn't at the very least. The diagnostic process should include the following steps:
- Perform a leak rate test: Freeze dryer integrity and leak rates are intimately connected. You can get a sense of both by running a leak rate test. The standard leak rate is typically less than 30 to 60 millitorr (mTorr) per hour. Should the number rise above that, your freeze dryer's integrity may have been compromised.
- Perform a pressure rise test: This companion to the leak rate test can also be used to identify leaks. You can run this test by closing the isolation valve between the freeze dryer chamber and the condenser and recording the pressure increase over a set period. If the pressure rises more quickly than it does during the drying process, then the dryer likely has a leak.
- Pinpoint leaks with isopropyl alcohol: If a leak has occurred, you can narrow down its location by applying isopropyl alcohol to common leak points while the dryer is under vacuum. Gaskets, welds and fittings are some of the most common. Check the vacuum reading after each application of isopropyl alcohol. If the vacuum reading jumps suddenly, you have found your leak.
- Inspect and tighten fittings and connections: The fittings and connections that bind the freeze dryer can grow loose over time, leading to small vacuum leaks. Checking hose clamps, sensor connections, chamber ports and other connections for potential tightening can resolve this issue.
- Check to see if the door and chamber align: The freeze dryer door and chamber can't compress the gasket evenly if they are misaligned. Check that the door aligns with the chamber and seals properly, as a misalignment can cause leaks.
If none of these practices help you identify the issue with the freeze dryer, it may be time to contact professional support. There are some steps you can take first to deal with specific problems.
Problem: The Freeze Dryer Has an Insufficient Vacuum
As stated, diagnosing freeze dryer malfunctions can be time-consuming. This is especially the case with weak vacuums. A faulty vacuum pull can be caused by the smallest compromise in the setup, from a microscopic hole in the vacuum tube to a faulty manifold valve. As such, locating the breach boils down to one thing: isolating components.
Isolating the Vacuum Pump
When your freeze dryer isn't pulling a vacuum sufficient for your application, you should first determine if the source of the problem is the freeze dryer itself or the vacuum pump.
Isolating the pump is simply a matter of:
(1) changing the vacuum pump oil and
(2) capping the vacuum inlet in the freeze dryer's chamber.
We recommend changing the oil three times, back to back, to ensure that all foreign moisture is removed before pulling a vacuum. Alternatively, you can buy flushing oil concocted specifically to rid the oil well of contaminants.
After depositing fresh oil and capping the vacuum inlet, activate the pump and monitor its strength. If the pump is strong, then the compromise originates with the freeze dryer.
However, if you've followed all of the above steps and you still have a weak vacuum, then either the tube or the pump itself is the source of the problem. Swap the tube and run another vacuum pull. If it's strong, then you simply need a new tube.
But if the vacuum pump is still struggling at this point, it's safe to conclude that the pump is the problem. You'll either need to rebuild your pump or purchase another one.
Isolating the Freeze Dryer
So you've determined that neither the vacuum pump nor its tube is the source of the leak. This can only mean that the leak originates in the freeze dryer's chamber or its manifold. Now what?
You must continue whittling down to the source by isolating the chamber. You can accomplish this by plugging the port that leads into the manifold, then pulling a vacuum. If the vacuum is weak, then you'll likely have to replace the door gasket. If it's strong, then that leaves just the manifold in the list of potential culprits.
Should the leak come from the manifold, you'll then need to test the valves — or, more specifically, their plastic selector knobs. Those plastic parts corrode much more easily than the rubber valves themselves, so in most cases, the knobs are all that will need to be replaced.
To test the valves, remove each one, cap the outlets and pull a vacuum. If the target vacuum is reached, then one or more of the selector knobs is faulty and you'll need to order new ones. Here's a guide on how to quickly and easily locate faulty valves with nothing but foaming hand soap.
While unlikely, it's also possible that one of the manifold tubes could be the source of the leak. Occasionally, the welding in a manifold can have tiny pinholes that allow pressure to escape. This can only be ameliorated by re-welding the joints or by purchasing a new manifold entirely.
Problem: The Freeze Dryer Does Not Reach the Proper Temperature
Sometimes freeze dryers have no problems holding a strong vacuum, but don't drop the chamber's temperature far enough. Luckily, tracing the origin of such an issue is considerably simpler than tracing that of a weak vacuum:
If the problems occur after a defrost, your defrost valve is stuck. Otherwise, there is a problem with the freeze dryer's refrigeration system. Unfortunately, refrigeration issues can be very difficult to resolve, so you are likely best off hiring a qualified technician to repair it for you.
When to Work With a Professional
The above maintenance methods are extremely helpful, but at some point, you may run into an issue that you can't solve yourself, such as a faulty refrigeration system. Maybe your freeze dryer is making a noise that you can't identify, or an internal mechanism may break or shut down entirely. It may overheat no matter what you do or fail to dehydrate items fully.
Don't be afraid to ask for technical support in cases like these. Maintenance technicians can save you time and money by quickly identifying issues and repairing the dryer accurately. They can also answer common questions about your machine's life expectancy and its current health.
Find Used Freeze Dryers and Other Equipment at New Life Scientific
If you're in search of quality freeze dryers or other equipment at prices you can afford, New Life Scientific is the partner for you. We provide used lab equipment to colleges, biotech companies and more.
Every piece of equipment is tested in-house to ensure its quality before we send it to you. We also offer a 90-day warranty, so you know you're getting your money's worth.
To learn about our used equipment, including freeze dryers, fill out our contact form or give us a call at 567-292-2752.
