A few years ago picked up a dehumidifier, Haier for $39.99 @goodwill. It stopped dehumidifying. Bought a service port off fleabay $12.-.
Connected gauges. Seems the manufacturer ensured some kind of slow leak, there was zero pressure in the system. I had a can of R134A sitting on the garage shelf. Connected valve to can and to gauge set and nothing happened. Turns out somewhere along the years powers that be ordered a design change to the cans. They have a valve in them. The old system was, just pierce the can and go.
The valve I had was the piercing type. Too short to reach the valve of the can.
Off to the local NAPA, was lucky they had only one of the newfangled valve for the self sealing cans, also picked up a couple of more cans of R134.
Back home, attached vacuum pump, pulled the system down to clean out the air. Held vacuum for a half hour. Then connected refrigerant can. One and about an eight can got the eveporator to fully uniform cold. Put covers back on.
So 9.95 for a valve, 10.- for a can of R134 +tax and my now $~76.- dehumidifier is working again. + a few hours fo fiddling. And given that it took about 4 years to leak out, should be good for another at least 3. And now easily rechargable.
BTW originally the refrigerant was r410. r134 is better for cooling according to some wise men.