A space heater, left on 24/7, would run about $160/year in CA. Honestly, $300/month sounds part for an electric bill. I suspect there's no short to ground or wasteful compressor or anything like that, and it's just that he's using $300 worth of electricity a month.
What are the electric rates in CA??? A typical space heater uses 1.5kw. In 24 hours it has used 36kw/h. In 356 days it has used 13,140kw/h. At 10 cents per kwh that's $1314 per year.
