The compressed air leaving the compressor is normally around 65-75C which contains a lot of water vapour and once that comes into contact with pipework/air tanks etc it cools rapidly and turns back into a liquid water. To dry the air we would install a refrigerant dryer and filters to remove the majority of the water from the compressed air.
If you already have a refrigerant dryer and filters it worth checking whether it’s switched on! I know obvious but it’s amazing how many call outs we’ve been to where this has been the case. Otherwise the filters need checking for blockages and/or the gas in the fridge maybe low. Either way you can call our refrigerant engineer to come and have a look for you.