G TWO AIR CONDITIONING PACKS WITH 131-96 AUXILIARY POWER UNIT (APU). SERVICE RECOMMENDED LETTER MOS 03-JUN-1998 - (s) SL 737-SL-49-061 131-98 APU START CONVERTER UNIT MODIFICATION. SERVICE LETTER RECOMMENDED MOS 10-JUL-1998 - Is) SL 737-SL-49-067 131-98 AUXILIARY POWER UNIT ELECTRONIC CONTROL UNIT (ECU). SER