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:
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.