Filter driers are used in refrigeration and air conditioning systems to filter unwanted solids and moisture from the system.
Moisture will block a system at the expansion device as it turns to ice and will cause the oil in the system to become acidic. Acid within a system will break down the compressor windings and cause the compressor motor to burn out.
Filter driers are made speciﬁcally for different parts of a system, liquid and suction ﬁlter driers are the most common types.
Hermetically sealed ﬁlter driers with ﬂare or solder connections are used in small to medium systems with pipe diameters up to 3/4 inch and solder connected demountable (pull apart) shells with replaceable ﬁlter drier cores are used in larger systems and pipe diameters or 7/8 inch and above.
There are two types of internal ﬁlter drier media in common use, molecular sieve and activated alumina. Molecular sieve has very high moisture holding capacity while activated alumina has a high acid holding capacity.
It is common for original equipment manufacturers (OEM’s) to use activated alumina in ﬁlter driers as the manufacturing environment can be controlled to minimise the introduction of moisture.
Field replacement ﬁlter driers are often a mixture of molecular sieve and activated alumina to ensure both moisture and acid are removed from the system.
Compacted bead ﬁlter driers are usually made from a mixture of molecular sieve and activated alumina and are the most commonly used service replacement ﬁlter driers. The advantage in service replacement is if moisture is present, then acid will be too. So capture of both moisture and acid is required to effectively remove contaminants.
Solid core ﬁlter driers use a bonding material to produce a solid core, this type of core is used on some hermetically sealed and all demountable ﬁlter drier shells.
Compressor motor burn outs contaminate the system so after replacing a compressor a suction burn out ﬁlter drier should be installed in the suction line. This burn out ﬁlter drier should be removed after the system has operated for some weeks to ensure all the acids and other contaminants have been affectively removed from the system, this will protect the replacement compressor.
One of the most common causes of damage to refrigeration and air conditioning systems is moisture in the system. Moisture can be introduced during open maintenance procedures so ensuring a good vacuum after maintenance and replacing the liquid line ﬁlter drier is essential to ensure future reliability.