Automotive A/C systems must have a means of trapping and holding moisture that may get into the system. One way of doing that is by using a receiver drier. The drier is usually located on the liquid line of the A/C system, between the condenser outlet and the evaporator inlet.

Driers perform a few different functions on the A/C system. First of all, they are a storage tank for excess refrigerant. Under certain operating conditions where heat loads are reduced, the evaporator does not require the same amount of refrigerant as when heat loads are extremely high. In those cases, the liquid line receiver drier will hold excess refrigerant.

The drier will also trap moisture in the system. Using a drying agent like silica gel desiccant, the drier forces the flow of all refrigerant through the filter section in order to be drier. That filter section also includes other filter media that will trap and hold debris and other contamination that may be in the system.

Driers can become restricted or plugged if those filters trap an excess amount of contamination. Also understand that the drying agent can only hold a fixed amount of moisture. When that level is attained, the moisture will continue to trave throughout the A/C system, mixing with the refrigerant to form harmful acids that will corrode other components internally.

Driers are not to be confused with Accumulators. Driers are always on the high side of the system while accumulators are typically mounted on the low side of the system, usually right at the outlet of the evaporator.