Dehumidifier frosting up
It needs gas.
Quite simply the only way it can freeze up is when the refrigerant gas is getting low to the point when it starts super-expanding at the evaporator.
Any authorised refrigeration technician should be able to top it up, and check it for leaks - there may be a seal that is partially shot, or possibly a leaky joint / pipe / compressor. A refrigerant leak detector will track this down quickly.
Only thing is - get a quote for the work first - sometimes refrigerant is pricey enough to make it close to not worth it on some units.
Unfortunately this is not something you are permitted to do yourself (topping the gas up, not the leak checking) due to environmental legislation.
Good luck, it should be worth doing, otherwise it will probably continue to get worse until the compressor fails, maybe quite quickly.
Hope this helps :)
on Apr 07, 2017