Devotees' cooler suit (3,4)
I believe the answer is:
fan club
'devotees'' is the definition.
(I've seen this before)
'cooler suit' is the wordplay.
'cooler' becomes 'fan' (something which cools).
'suit' becomes 'club'.
'fan'+'club'='FAN CLUB'
(Other definitions for fan club that I've seen before include "Organised group of admirers, as of pop stars" , "Admiring band" , "Association of ardent followers" , "Association of devotees" , "Fervent admirers" .)