The 135R/T has two APU's. They're called a QSAS, Quick Start Auxillary System. They sit side by side in the aft part of the cargo deck in an enclosure cabinet just infront of the boom pod. The inlet and exhaust are both on the left side of the fuselage. The 135 is completely self sufficient and requires no ground equipment to start engines. The QSAS has one generator mounted on either of the APU's, usually the number 1 APU which is the one furthest aft, to provide the aircraft electrical power. It also provides air to the main engines for starting.