I was able to completely rebuild my Dyson vacuum cleaner, with Dyson parts for a fraction of a new one. My A/C had a control board that went out, and only an authorized dealer could sell a replacement. The catch was, the dealer had to install it. So, since I have the skills, so I thought, I pulled the board, and went to repair it myself. They wanted to charge $1100, when the bad part was $7 dollars including shipping.
But guess what, they have a battery backed latching relay to detect if the boards are disconnected. Those MFr's. I replaced the entire system after this fiasco. There is an Asian company that made fighter planes that escorted bombers to Pearl Harbor, that now make HVAC systems. I would avoid them.
Making your products proprietary is one thing, but intentionally engineering them this way is criminal.