Ultralow freezers, which typically operate at -86˚C, are used in laboratories and hospitals worldwide and are intended for reliable and long-term storage of temperature-sensitive research samples such as blood, plasma, and organ tissue. However, as with any essential piece of laboratory equipment, failure to follow best practices will result in sub-optimal performance, and may be detrimental to precious sample material as well as to the freezer itself. Implementation of preventive maintenance measures will help to ensure that an ultralow freezer remains in a satisfactory operating condition, and will avoid unnecessary shortening of the usable lifetime.
Although servicing and advanced maintenance of laboratory equipment should always be performed by a trained service technician, there are a number of ways in which end users can carry out preventive maintenance of ultralow freezers. Preventive maintenance involves routine inspection of equipment, and allows any possible sources of failure to be detected and corrected in a timely manner. Just a few simple activities can ensure optimal freezer performance, minimize energy consumption, and will ensure that the manufacturer’s warranty and compliance are met; we’ve detailed some of the main actions here.
Repeated opening of the freezer door may result in a build-up of frost or ice, which can stop the outer door from sealing properly; it’s therefore good practice to inspect the door seals and gaskets for ice build-up every time the freezer is opened. “To help minimize ice build-up, we try to get samples in and out as quickly as possible, but also scrape the ice away from the door seals every two weeks and make sure that the ice does not build up on the inner doors,” says Tim Avis, research scientist at Discuva. “Every year we have a general clear out of old stocks, and use this opportunity to defrost the whole freezer.”
The condenser is one of the main operating components of an ultralow freezer, and functions to transfer heat from inside to outside. If dust is allowed to build up on the condenser filter, the ability of the condenser to transfer heat to the ambient environment is compromised; it’s therefore important that the filter is cleaned regularly. “To help maintain the efficiency of the freezer, we clean the filter once a year,” adds Avis.
The function of a freezer gasket is to form a tight seal around the edge of a door, preventing warm air from entering the chamber or cold air from leaving. All ultralow freezers are fitted with an outer door gasket as standard, however many manufacturers also gasket the inner doors to help maintain a uniform temperature within the internal compartments of the freezer. “I regularly check the door gaskets for leaks,” says Adam Hudson, scientist at LGC Limited, “which can easily be spotted by an accumulation of ice at any weak points. I also wipe them down with a soft cloth occasionally, to remove any dust or dirt that could compromise their performance.”
Ultralow freezers perform best when the airflow within them is uninterrupted, and the use of a racking system not only maximizes storage space but also ensures that the correct airflow is maintained. “We use a freezer racking system to allow us to easily locate our samples,” explains Giovanna Cacciola, senior scientist at Innova Biosciences. “This permits us to stack boxes and containers neatly, and means that the amount of time for which the door remains open is kept to a minimum.” It is also important that materials are not stored on top of the freezer, since these can trap warm air and cause the compressor to operate more frequently to maintain temperature; not only will this raise energy costs, it will also reduce the lifetime of the compressor.
Ultralow freezers are fitted with alarms to indicate high temperature, low temperature, power failure, prolonged door opening, system monitoring failure, and more. Although these can usually be muted, it is essential that they are not ignored. “The ultralow freezers which I use are all equipped with an alarm test button,” notes Hudson. “The alarm is checked routinely within the cleaning and maintenance schedule, and each freezer is clearly labeled with the details of a point of contact.”
Ultralow freezers contain irreplaceable samples, costly reagents, and often years of research. By treating them with the respect they deserve and performing simple preventive maintenance, these vital pieces of laboratory equipment will provide many years of reliable service.