What does the AC receiver drier do?

Should I replace my a/c dryer when I replace my compressor?

The filter drier is a device that removes foreign matter from the refrigerant. This foreign matter can be dirt, filings, moisture, parts, and acid caused by moisture.

Some sources of moisture in the refrigeration systems include poor service practices, air trapped from improper evacuation techniques, leaky systems, and improper handling of lubricants.

Filter drying operations are accomplished with a variety of materials that are packed inside the drier. Some manufacturers use chemical beads and some use porous blocks made from a drying agent.

The most common agents found in filter driers are:

Activated alumina.

Molecular sieve.

Silica gel.

Silica Gel: It’s a no crystalline material with molecules formed by bundles of polymerized silica, forms a weaker bond with water, which is why silica gels are not widely used in modern filter driers.

Molecular sieve dessicants: Are sodium alumina-silicates in cubic crystalline form. The crystal structure is a honeycombed with cavities that are uniform in size that can selectively absorb molecules based on their charge (polarity) and size. These properties allow water to be absorbed while still permitting the larger molecules like refrigerants and their lubricants to pass by. The surface of the desiccant is coated with cations, which are positively charged and act like magnets to attract polarized molecules such as water. Molecular sieves retain the highest amount of water and keep the concentration of water in the refrigerant low. The molecular sieve filter is recommended for use as liquid line filter driers because of these good water-removal capabilities. The strong bond between water and molecular sieve thus keep the occurrence of system corrosion, acid formation, and freeze ups very low.

Inorganic acids like hydrochloric and hydrofluoric acids are formed when high system temperatures break down refrigerants and water. These acids can attack metal surfaces in the system and destroy the crystalline structure of the molecular sieve.

In the presence of the wrong desiccant and water, organic acids can then form from the broken down refrigerant lubricants. Organic acids, sludge like material, can plug up metering devices.

Activated Alumina: It’s formed from aluminum oxide. It is not a highly crystalline structure like a molecular sieve; its pores vary in size and do not absorb molecules based on pore size. Because of this ,it can absorb much larger molecules like refrigerants and lubricants along with water. Activated Alumina is even more effective in removing  organic acids when it is used in the suction line of the refrigeration system. This is why some manufacturers recommend using a suction-line filter drier made of activated alumina for acid cleanups.

Filtration,another main function of a filter drier,can also be done with a screen.A screen will filter or catch particles that cannot fit through its wire mesh.As particles and contaminants start to cover the mesh of the screen,they act as a fine filter that removes even smaller particles.

Filters may also include the following:

Bonded desiccant cores

Fiberglass pads

Rigid fiberglass with a resin coating. 

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