BMW original Behr A/C Receiver drier. Located in the high pressure side of the air conditioning system, the A/C receiver drier serves two basic purposes. The first function is a basic reservoir to store extra refrigerant and oil. The other purpose is to contain “desiccants” that absorbs water out of the compressor oil and refrigerant. Every time the system is opened, the drier should be replaced to avoid further exposure to water and breakdown that can clog and damage A/C components. When water is allowed to combine with the refrigerant, it becomes damaging hydrochloric acid.