Sounds as if someone cut corners when wiring the AC system. Central air conditioning should had been 220V and dedicated, both evaporator and condenser. Cost effective way around it is like Rodman suggested...a power conditioner.
Power line noise from appliances
Living in rural New England, I've always had good power until this year when I added central air to my house. There are 2 20-amp breakers (one for the air handler and one for the outside compressor) which when on, seem to inject high frequency nasties in my audio system. I've had less than favorable impressions conditioning the audio system and I am wondering if anyone knows how I could filter the noise at the source i.e. isolate the two breakers for the a/c from the rest of my system, so that I can prevent the high frequency gremlins from the a/c system polluting the otherwise relatively clean feed to my audio system.