LEYDEN, MA (FRANKLIN COUNTY NOW) — An exterior air conditioner unit caught fire at a home on Greenfield Road in Leyden Thursday evening. Crews were dispatched to the scene at 5:05 p.m. and found a burned thermostat and the A/C fire, caused by a mouse nest in the A/C unit. Firefighters from Leyden, Bernardston, Colrain and Bernardston police responded to the scene.