The most common issue is the leaking compressor component for your case.  Adding 氟 is not going to help and 氟 will be leaking anyway.
if it is in 5 year warranty for your compressor, you need to get diagnois reports from approved service company.  It will cost about $50.  If the compressor is not under warranty or if the defects are also from other components out of warranty, the repair itself will cost you $200.  In this case, you had better buy a new dehumidifer.