Some years back, we rented one of those carpet cleaning machines from a local store. It was a HOT day...and we had the a/c on. Never used one before. First time, the water turned black...but we did not notice any improvement. Waited a bit...then did it again. Nothing noticeable. By the 3rd time, we saw "something",...good. By the forth application, the carpet looked good. Fifth...almost new. It took almost the entire afternoon, given the time between applications. But..it did work and worked fine.
This past fall...I found a local carpet store that cleaned carpets. INCLUDING RVs.! I drove the RV to the shop one Saturday morning (had an appointment, of course) and 2-3 hours later...and $90 I had carpet that looked just about brand new.