Home AC System

If he knows anything about electricity, have him check the voltage. Thermostats run on low voltage through a step down transformer. Something is wrong with the combination it seems.
Update, talked to my brother and law and he said that the guy that installed his new system switched to a different company for the thermostats and he hasn't been happy with them. He's going back to the brand that he's used for the last 10 years, why change suppliers when you are having good service with what you were using? Guess the guy was trying to save a few bucks and wound up losing money by changing out junk thermostats