When should you repair an AC unit instead of buying a new one?

The choice between repairing and replacing your AC unit can have a big impact on your homeownership costs. Catherine Lane/Getty Images Few household problems create more frustrations or more sticker shock than a malfunctioning air conditioner. One day, your system is keeping your home comfortable without issue, and the next you're facing an unexpected service call, a costly repair estimate, or, in some cases, a recommendation to replace the entire unit. …