Trouble with new AC

It's ssooo much easier to trouble-shoot this type of system if only each A/C unit was wired totally independent of each other. Yes, each one with its own thermostat(including ON/OFF switch). I modified the system in my Dutch Star back when it was only 4 months old. I had a terrible experience (going from Arizona to New Mexico), and both units failed. Under warranty, I could not find any approved shop that could look at it right away. I was so motivated(under those hot-weather conditions) that I decided to learn how the A/C control system was designed. When I learned that they were not independently wired(both were controlled by the front-unit circuit board) I couldn't believe it. I modified it myself, and never had a control problem since.
In your case, you gotta find a genuine expert in order to find the cause of your problem.