Used to store precious, often irreplaceable samples, ultralow-temperature (ULT) freezers are an essential workhorse of laboratories worldwide. When used and maintained properly these specialist units typically provide 10–12 years of highly reliable service, but to get the best out of them it is important that they are treated with respect. This includes locating them wisely, ensuring they are provided with a power supply of the correct voltage, and performing essential preventive maintenance functions to keep them running optimally. We spoke with Adam Christensen, technical support/service trainer at NuAire, who shared with us his expertise in ULT freezer preventive maintenance.
“For maximum performance and efficiency, it’s recommended that a ULT freezer is checked and calibrated periodically by a qualified service technician,” he says. “However, regular cleaning and maintenance is relatively straightforward and can easily be performed by the end users. We suggest adopting a number of simple practices to extend freezer life. By making these routine it’s possible to detect and correct any potential sources of failure in timely and efficient manner.”
“Although gradual formation of frost or ice within the inner chamber is inevitable, this can be kept to a minimum,” explains Christensen. “The room in which the unit is situated should have an ambient temperature no higher than 32oC, while exposure to direct sunlight and drafts or heating/cooling vents should be avoided. It’s also important to provide suitable spacing around the unit for effective ventilation.”
Further steps to lessen frost or ice build-up include minimizing the number and duration of door openings and checking that the door latches securely upon closure. “Periodic removal of frost or ice build-up from the door gaskets and inner chamber can be achieved by scraping,” notes Christensen. “The vacuum relief port should also be cleared regularly.”
“We recommend fully defrosting the chamber at least twice a year depending on usage and environmental conditions,” says Christensen. “This involves transferring all contents to another ULT freezer, switching off the unit, then wiping it out with a non‐chloride detergent once it has defrosted. This can be a good time to inspect door gaskets and make sure they seal properly, to clear out old stock, and to re-organize existing samples to maintain correct airflow and afford better accessibility. The unit should then be allowed to operate empty overnight before being reloaded.”
By transferring heat from inside the ULT freezer to outside, the condenser has one of the most important roles to play in ULT storage. Christensen explains that dust accumulation on the condenser filter can compromise its performance, adding that the condenser coil also requires regular preventive maintenance. “We suggest cleaning the condenser filter every two to three months, more frequently if the environment is particularly dusty, and the condenser coil at least once a year,” he notes.
“If frost and ice build-up isn’t removed from the inner and outer door gaskets, they can tear,” says Christensen. “This compromises the performance of the unit. Leaks are usually indicated by a streak of frost at the point of gasket failure, but by wiping down the gaskets with a soft cloth at least once a month, tearing can be avoided. Furthermore, frost and ice build-up around gasketing can wear out the outer door latch since it makes it hard to close the door.”
ULT freezers are often fitted with alarms to indicate a variety of sub-optimal operating conditions. These can include high temperature, power failure, low battery life, prolonged door opening, and system monitoring failure. According to Christensen, knowing what the different alarms mean facilitates swift remedial action. “It is imperative that alarms are not ignored and that a plan of action is in place for situations that require operator input. This includes labeling each freezer clearly with the details of a point of contact and back-up contact and having spare ULT freezer space available should there be a need to transfer samples to an alternative unit.”
Freezer alarms will still occur during a power outage since the display and buzzer are powered by a battery. Christensen says this should be replaced by a certified technician every 2.5 years, when the battery timer will also be reset. “The battery life of NuAire freezer alarms can be checked by entering the function code menu, however it is sufficient to simply have the battery replaced once the 2.5 years expires and the light is illuminated,” he adds. “Checking the battery timer in the function menu can be incorporated into routine cleaning and maintenance schedules to provide end users with additional peace of mind.”
A wide range of ULT freezers are available, yet they all have one thing in common—they require care and attention to keep them performing at their best. Just a few simple preventive maintenance steps will ensure the longevity of sample material while maximizing the lifetime of these vital pieces of equipment.
The Blizzard™ NU-99420 14.8 cu. ft. (420 L) -86°C Ultralow Freezer
The Blizzard™ NU-99728 25.7 cubic feet (728-Liter) -86°C Ultralow Freezer
For more information on ultralow freezers, download The Essential Guide to Ultralow Freezers eBook