Crandall

Crandall was a Human woman, a Starfleet officer who manned life support operations aboard the USS Enterprise (NCC-1701) in the 2260s.

History
In 2269, when a magnetic organism seized control of the Enterprise and shut down life support on decks 5 and 6, James T. Kirk asked Crandall to repair those systems immediately, and she was authorized to call upon any personnel she needed. The crew in those sections ended up having to wear life support belts. 

Background
It was possible but unlikely that this Crandall was Julia Crandall. Julia transferred off the Enterprise in 2267 and Pavel Chekov did not see her again prior to her death in 2290. Julia would have had to transfer back only while Chekov was absent for Starfleet Security training.