What was found
Flt #37, JFK to PBI, Burning smell in flight, no visible smoke. vent extract fault in flight, 2 min later, aircraft RTB to JFK, emergency declared, met fire department, JetBlue emergency procedures followed.Inspected and found the extract fan seized. Removed and replaced the extract fan, fan worked. IPW 21-26-51-401, Ops check IPW 21-26-710-001, Ops check good, no defect noted.