PTC - positive temperature coefficient heating element. It has been a weak link in early S’s and 3’s. There are pending legal issues as some folks believe it should be covered by the battery warranty given the location of the module. It costs 2k to fix in the S’s and over 1k in the 3’s… Sounds like Tesla is now doing what a normal repair shop would do: make the needed repairs without replacing everything. In so doing, the price went down and they are trying to get this weak point (and the warranty issue) off the radar.
A video to learn about the PTC or even to learn to do it yourself (300 is a better deal).