Hereis a cut n paste of how I would handle carpet cleaning. I have posted this on other forums. If you follow the procedure I have outline here you will get good results.
Since I have seen and read several threads on carpet cleaning, thought I would chime in. Ive been in the carpet cleaning business for years. Im also certified by the International Institute of Carpet Cleaning and Restoration. Can't say Im a real big fan of cleaning carpets with Oxy clean. I don't use it and know for a fact none of my friends in the biz use it either. Many reasons why, the most prominent one is the amount of calls I get from ladies who spray it on a stain, walk away and a week later her carpet has discolored. She sees the ad on television when the guy pours it on and it "disappears". I see this all the time. Not trying to bash anyone using it but if you guys are using this stuff, better make sure you get it rinsed out completely. While I do not clean cars (only my own), here is how I would do it. These principle are the same for cleaning home carpets and the principles taught to me by the IICRC.
#1 Vacuum thorougly. Getting loose dirt is critical to the end result
#2 You need to apply a good prespray. What is a prespray? In our business its called a Traffic Lane Cleaner. You spray it on the carpet to dissolve dirt and stains. That simple. There are many good ones out there. Ones I would look at are: Prochems Ultrapac, Chemspecs Express Lane or Matrix Grand Slam. Most of these run about $25.00 a gallon, but the dillution rations are usually 4 oz per gallon or 1 oz for a 32 oz spray bottle. There are many places on the web to find these presprays, one that comes to mind is
www.jondon.com. Ive used them, they have good customer service. A gallon would last a long time. I use a cordless sprayer but for cars a trigger sprayer would work, although a pump up sprayer from Sears or Home Depot would be quicker. Always apply your prespray with HOT water. Hot water breaks down grease and grime twice as fast as cold water.
#3 Agitation. Once the prespray is applied, you need to agitate it into the carpet. Its like shampooing your hair. You wouldn't dump shampoo on your head and not scrub it in your hair. Same principle applies to carpet cleaning. I prefer a horseshoe brush for this. I would not take a scrub brush to someones car seats.
#4 Dwell time. Need to let preprays dwell on the carpet for a minimum of 10 minutes maybe longer depending on how dirty the carpet is.
#5 Extract. This is when good equipment is essential for a quality job. You have all heard the term "Steam Cleaning". Well, all that is is water going into the carpet and extracting at the same time. We use water at 210 degrees to accomplish this. However, I realize most of you probobly cant extract like this. If it were me and I was detailing alot of carpets, and wanted to be a cut above my competion I would invest in a good portable extractor. No, the are not cheap. A good one will run $650-$1000. However you do it, you must rinse these cleaning agents out of the carpet. If I were using a shop vac, I would mist hot water on top of the prespray (after it dwells) and rinse it out.HOTTEST water you can find. Whatever you can find that gives you the most suction, use it.