Moisture is an enemy of every refrigeration system. Even a few drops can freeze in a capillary tube or expansion valve, react with oil to form acids, and attack the compressor motor windings. The filter drier sits between the condenser and the metering device and contains a molecular sieve that holds water, plus a filter that catches particles.
The drier is meant to be replaced, not reused. Whenever the sealed system is opened, for a leak repair, a compressor change or a recharge, a good technician fits a new drier matched to the refrigerant and pulls a deep vacuum before charging. Leaving the old drier in after opening the system is a common shortcut that leads to repeat breakdowns.
Moisture risk is higher during the monsoon, when humid air can enter quickly through an open system. A drier that is noticeably colder at its outlet than its inlet, or frosts over, is often partly blocked and restricting flow.