All-time summertime heat records keep giving in the weight of increasing global temps-- a trend that strikes house, literally and figuratively, when you receive your monthly cooling bill. Errors you're making with your house AC may be damaging its performance, effectiveness, and safety, experts say.

If you have a severely maintained system, it can end up being contaminated with bacteria that might be hazardous if inhaled. Common signs are asthma problems and allergic…