It has to be frost free or the cycle wont work. The concept of the cabinet detailed above doesn't care if you need to add humidity or reduce it. It's a closed cycle;
Heat source adds heat....
Temp controller turns fridge on....
Fridge reduces heat and also humidity
Humidifier adds humidity
Process continues until fridge/humidifier stop...
Heat source adds heat.
That's a fairly simplified explanation. I use the same cabinet to do fermentation and curing...so the "cycle" differs at different stages. i.e. during fermentation the fridge rarely turns on, as I want high temps and high humidity. I just set the controllers at the appropriate settings. Once fermentation is done..i change the controllers to "Curing mode"..i.e. lower temps/humidity.
Please understand that this is a "band aid" solution. Ideally, as in the old world where temp and humidity ( and members like Wheels and Brican came from
) were part of the environment, that's where the product was made.
Anyway, i digress. The humidistat that I have only lets you have one setting. Humidify or dehumidify. I'm not aware of any off the shelf devices that do both simultaneously. It could be done, but would require some fancy PID control...of which I am planning
Sorry for being so long winded.