Air-con adjusted with a rare instrument (7)
I believe the answer is:
ocarina
'rare instrument' is the definition.
(ocarina is a type of instrument)
'air-con adjusted with a' is the wordplay.
'adjusted with' indicates an anagram.
'air'+'con'='aircon'
'aircon' mixed up with 'a' can make 'OCARINA'.
(Other definitions for ocarina that I've seen before include "we blow it" , "Small egg-shaped wind instrument with holes for the fingers" , "Flute-toned musical toy" , "Simple wind instrument" , "toy instrument" .)