If an air-conditioning system malfunctions or isn’t properly maintained, it can become contaminated with infectious microbes, says a microbiologist. LEICESTER, England: Air-conditioning can feel heaven-sent on hot summer days. It keeps temperatures comfortable and controls humidity, making indoor environments tolerable even on the most brutally warm days. But some people avoid using air-conditioning (AC) no matter how hot it gets outside, out of fear that it will make them sick. While this may