POULSBO — A malfunctioning air conditioner caused a fire that destroyed a $263,000 Kitsap Transit bus Friday night in Poulsbo, according to the Kitsap County Fire Marshal’s office.

Deputy Fire Marshal Tina Turner said mechanical failure in a condenser unit sparked the blaze, which was reported by a security guard at about 10: 40 p.m. The bus was parked inside a Kitsap Transit garage on Viking Way near Vetter Road.

Poulsbo firefighters kept the fire from spreading to nearby buses, though windows on a nearby bus were cracked, said Hayward Seymore, who oversees fleet maintenance. Seymore said insurance investigators are still looking into the fire but the bus appears damaged beyond repair.

Kitsap Transit purchased the 40-foot coach in 2003. It was one of about 30 buses parked in the Viking Way garage overnight.

Seymore said Kitsap Transit is inspecting other buses of the same chassis for signs of mechanical failure. This week he also began instructing drivers to turn off power from their bus’s batteries at night to prevent electrical fires.

Kitsap Transit has spare buses to substitute, so the loss of the coach shouldn’t effect service, Seymore said.