puritan bennet sandman cpap

hello every one i have bought a P,B, sandman model m-148ofudo-30 unit and to my surprise this unit has no humidifier chamber only a sponge inside were the water chamber unit should be it is a new unit and functions well .,but is it possible that the sponge acts as a humidity chamber or is this CPAP unit chamber free and i sleep dry ., any help with this i would love to know thanks.

Go here and request the manual via email and see what it says.
https://www.apneaboard.com/adjust-cpap- ... tup-manual

This is a discontinued machine. However, like anything else that is discontinued, it can continue to run and do the job it always did.

You should be able to order a water chamber from the internet if your DME won't give you one.