Turning off air conditioning units while your away from home can save money and energy. It can also cause mold problems in houses in humid environments and lead to wear and tear on air conditioning systems that requires frequent repairs. That’s one reason experts recommend simply setting the air conditioning up a few degrees when leaving the house. Patrick Phelan, a professor in the School for Engineering of Matter, Transport and Energy, part of the Fulton Schools, suggests using “smart thermostats” equipped with sensors that can monitor a house’s occupancy and raise the temperature when no one is home to conserve energy and lower temperatures when people return.