can my landlord charge me because of this?

This sucks. I would

1) Document everything. Every conversation I had on the topic, I would repeat in email to the "tenant in charge" or to the landlord.

2) Take pictures of the carpet, including parts of the carpet that weren't clean.

3) Talk to the real landlord.

4) Look into talking to a lawyer.

Make sure the timeline is clear documented in writing (i.e. mold 1 day after cleaning).

When I write letters about these issues, I always keep in mind that I am writing for a judge. What I write is addressed toward the person with whom I have a conflict, but everything I write is keeping in mind that the important person it the judge who will be reading these letters if this ever goes to court. Make sure that everything is documented in writing.

everything is in text, so just have to get pictures of the floor then

I would rent a dehumidifier and run. it a couple days to see how much moisture can be drawn out of the room. Where I live, the summers are exceptionally humid and the dehumidifier keeps us from drowning in mildew. It wouldn't hurt to call a cleaning specialist like ServePro...I've used them to clean up a flooded basement 'soaked carpet and books' and for cleaning up my parents house after all of the heating oil leaked out of a fuel line into the house during my Dad's funeral.

Plus, you should ask him for proof of carpet cleaning over the last nine years. Most landlords know they have to replace carpeting every 5 to 7 years...so it's more of a landlord problem or responsibility...Don't hand over any cash to your roommate until you are positive it's the renters responsibility and the money actually reaches the 'real' landlord.

Don't know what state you are in but in CA I cannot charge a tenant for normal wear carpet problems if the carpet is more than 5 years old. Stains or rips are a different story. BTW. using a normal carpet cleaner that is functioning properly will not soak a floor enough to cause mold. No your roommate cannot charge you unless there is a sublease of some sort signed by you with the roommate. Whoever signed the original lease is the only one that can be charged by the landlord.. This is from experience kicking people out, renting several houses and in the legal field.