A CRJ200 with a pack MEL'ed inoperative filled with a strong odor filled after takeoff when the crew switched bleed sources from the APU to engine. An emergency was declared and the aircraft diverted to a nearby airport.

Narrative

Departed Flaps 20; Flex Takeoff. Aircraft was being operated under MEL 21-51-01 for right-side pack inoperative. MEL procedures for operation were reviewed. On climb out pilot flying called for After Takeoff Checklist; pilot not flying initiated bleed transfer from APU to Engine 10th Stage Bleed Air. L Pack Hi Temp Amber Caution Message displayed. Pilot not flying referred to QRH procedure for L Pack Hi Temp. PM switched bleeds back to APU. PM once again attempted to transfer bleed source from APU to engines. 10th Stage bleed source would not supply bleed air to operative (L) pack. Bleed source selected back to APU. During the cycling of bleed air source a strong odor was detected by PF and PM. The Captain contacted the Flight Attendant asking if the odor was present in the cabin. Flight Attendant responded yes. Odor quickly dissipated. Captain and First Officer discussed options and for safety and precautionary reasons; declared an emergency and requested/landed at nearest suitable airport. No passengers reported ill. Flight crew had no ill effects from odor. After landing emergency response met aircraft and determined no smoke/fire visible from aircraft. Contract maintenance personnel and flight crew performed operational check on aircraft per Company Maintenance Control. Could not reproduce Left Pack Hi Temp or odor associated. Maintenance control and Captain are discussing possible causes of odor source.