I've been experimenting and have an update on what I learned in my DIY attempt to re-chrome small plastic AC ducts. (It works!)
Tools: I purchased and used a "gift pack" 2 iron set containing a Coverite Trim Sealing Iron & a Coverite 21st Century Iron marketed for the RC aircraft hobby. The smaller trim sealing iron comes with 2 heads, (I used the angled tip head), which are painted with what looks like Teflon but isn’t. After a couple hours at max temp the paint began to peel off and no longer glided properly during use. The temperature adjustment on that iron is maximum 305 F. The larger 21st Century Iron has a maximum of 390 F and has a Teflon coating that held up well. The chrome ribbon I used came from a company called Malahide located in Canada. They sell ribbons and card embossing equipment. They have outstanding customer service and I highly recommend them. I ordered the Premium silver ribbon in 1.5” width. Scissors and an eraser were used as well.
Preparation: I practiced quite a bit on the sides of plastic handled screwdrivers until I had a feel for the speed and temperature needed. The cleaner and smoother the surface of the object to be chromed the better the results will be. My attempts to go over factory chrome without prep resulted in a splotchy look. When I used an eraser as a mild abrasive to remove old plating and smooth the surfaces, I had much better looking results.
Process: After surface prep, I let the irons warm up to temp for about 5-7 minutes. I held and or taped a piece of the silver/chrome ribbon in place over the plastic AC vent and “ironed” over it. I noticed when my iron was gliding smoothly it wasn’t quite hot enough. When it felt slightly sticky as I moved it, it seemed to work great. To get radiused profiles covered well, I had to move the iron over it a few times with slight variances in the approach angle. When the ribbon appeared to stick to the surface, I slowly pealed it off and Walla the chrome was applied. It left the ribbon with a transparent area where the chrome was removed and transferred to the AC vent. It works best to not iron over wrinkles in the chrome ribbon. Doing so will leave small areas not covered that will need to be touched up with another pass.
Results: While using the small trim iron, my best results were had when it was set to max temperature, 305F. It worked but I had to move the iron at a very slow speed to get good adhesion. I also had to go over areas multiple times to get an even coating. I found myself wishing it would get hotter. The easiest and best looking results were accomplished using the larger 21st Century iron set at 350F. The larger iron is a bit unwieldly for the task but I was able to use it in tight areas with some practice and creative ways of holding the AC vents. I liked it best. The smaller iron would be ideal if it would get hotter and had a Teflon coating on the heads. The actual color is sparking silver chrome. The attached pictures may look like matte silver, but that is simply my poor photography. The new chrome twinkles and is shiny just like the OEM chrome. My unscientific fingernail scratch test resulted in durability comparable to the OEM finish. It was very good.
I would not recommend using this method for more than touchups on a large bezel. It’s a good method for DIY on AC vents though. I hope someone finds this useful. It was pretty easy, you can do it.