Unlike commercial A/C systems, auto A/C systems have to contend with moisture. That is because automotive A/C systems include flexible rubber hose sections that actually allows moisture to penetrate right through the hose.

At the molecular level, when the A/C hoses on the vehicle sweat, that moisture travels right through the hose because of osmosis. Once inside the A/C system, moisture and refrigerants mix to create a harmful acid that will corrode A/C components like the evaporator and condenser from the inside out.

The problem is actually two fold. The corrosion causes the A/C components to leak prematurely because they are being corroded. Secondly, that corrosion travels through the A/C system and plugs up passages for refrigerant and oil. As an example, that corrosion can quickly restrict an orifice tube. When that happens, the refrigerant flow through the system stops as well as the flow of oil to the compressor. Continued operation of the A/C system means that the compressor is running without cooling, which it gets from the low pressure refrigerant, and lubrication, which travels in the refrigerant as a mist.

Drying agents or desiccants are used in received driers and accumulators in order to trap and hold moisture in the A/C system so that the moisture does not have a chance to mix with the refrigerants and cause the chemical reaction resulting in acids. Driers and accumulators should be replaced every 3-4 years or whenever major A/C service is being performed, like changing a compressor.