Once we recieved and unwraped the A/C we realized that it required a control box that is sold seperately for more than $150. On closer inspection, the control box connects to the A/C via a four wire connection. 5v and Ground is supplied by the A/C main board and talks via a balanced (two wire) data connection. I didn't try to discover the protocol as our existing onboard control box communicated via dedicated signal lines at 12v. Three to be exact. 12v compressor command, 12v low fan, and 12v high fan. Also I have limited electronics toolset (which does not include an o-scope).

Now I have a problem. Upgrade our entire control system at a huge expense (we are poor BTW), get a different A/C unit at a huge expense (did I forget to mention we are pretty poor...), or I can get to hacking...

Well, the logical choice for me was hack the crap out of it...

And so it begins...