I have used my x10 system with lights and outlets through out the house for a couple of years without any issues. I installed a cr 234 x10 amplified coupler repeater and life was good. However, a month ago I had a new Carrier air conditioning and heat system installed and nothing has worked since. Sometimes some of the lights come on, sometimes they dont or only a few will come on. Also, if any one has any thoughts on Insteon? My X10 system currently is the ir543 with the pronto. I am thinking of upgrading, but don't know if this would fix my problems.

It sounds like you may have noise on the power line.  Try turning off each breaker until you do not have any problems, then identify any equipment that may be causing the problem and install a noise filter.  Is you Air Conditioning unit a whole house unit or a window unit?

The AC is a whole house unit. I know the breaker that a tried turning it off. It still didn't make a difference. I was wondering that even though it is off, can it still cause noise? Any suggestions for a good noise filter?

Since your Air Conditioning unit is a whole house unit, then I doubt that it is causing the problem.  If it is a noise problem, then do as I sujested earlier, start turning off breakers until the problem disapears, then turn the breaker back on and identify the device that is causing the problem, this could be a TV, DVR, UPS, Computer, etc.  Once you identfy the problem, you can get a Noise filter from such places as Smarthome.com