An air dryer assures that air is supplied at the proper dew point for the ultimate generator performance. However, like the PSA generator and air compressor, the air dryer has to be selected for the highest ambient temperature at the installation site to avoid that feed air with too high-water content getting to the molecular sieve:
The above graph clearly shows you that the air dryer capacity at a maximum ambient temperature at the installation site of 35 °C should be 50% higher than the requested capacity at 25 °C and at 45 °C you need an air dryer with a capacity which is even three (!) times larger than the dryer capacity at 25 °C.
Too small, dimensioned air dryers = irreversible damage to the molecular sieve in the long term!