Auto A/C Terms - Glossary
Desiccant

Automotive air conditioning system suffer problems when they get contaminated with moisture. That occurs over time as water droplets, at the molecular level, pass right through the membrane of the rubber hose. That water causes serious problems when mixed with refrigerants. That is why auto A/C systems require a desiccant or moisture absorbing substance to trap and hold that moisture.

Unlike commercial or residential A/C systems, the auto A/C system requires flexible tube sections because some components are mounted on the engine while other components are mounted on the body of the vehicle. In order to accommodate those requirements, rubber A/C hose is used to complete a lot of connections between various components. As an example, the A/C compressor will move because it is mounted to the engine. Engine torque causes the compressor to move. However, the A/C condenser is mounted to the body of the vehicle, right in front of the radiator. Therefore, the connecting hose assembly must be flexible so that engine torque does not cause the connection to rupture and release refrigerants. That is accomplished using rubber hose sections.

Most problems occurring in the auto A/C system are a direct result of moisture contamination. That is because moisture in the system could not be held by the desiccant. That occurs when the desiccant is full. Once that happens, the moisture is allowed to circulate with the refrigerant. When refrigerant and moisture mix, the resulting chemical reaction causes the formation of harmful acids. Those acids corrode the A/C system components from the inside. That causes premature leaks in components like the A/C condenser and evaporator.

What is worse is that the corrosion created by moisture and refrigerant mixing and causing the acids to form is also a contaminant in the A/C system. The corrosion travels through the system and will restrict filter screens on various components like the receiver drier or expansion valve. When that happens, the A/C system can no longer circulate refrigerant and A/C compressor oil properly. If allowed to continue, the A/C compressor can suffer catastrophic failures.

The desiccants in the auto A/C system are usually part of the liquid line receiver drier or the accumulator. Every auto A/C system has one, but never both. Liquid line receiver driers are located in the liquid line between the condenser and the expansion valve. The accumulators are usually located right at the evaporator outlet, or in the line between the evaporator outlet and the compressor suction side inlet.

Both driers and accumulators perform the same basic functions in the auto A/C system. They store some refrigerant, they filter contaminants and they hold a desiccant that should trap and remove moisture from the system. However, it must be noted that each drier or accumulator has a fixed amount of desiccant allowing it to only hold a specific amount of moisture. When that level is exceeded, the moisture contamination in the A/C system takes place and the cost for clean up, flushing and repair usually outweighs the cost of regularly replacing the drier or accumulator.