Zealot's found in cooler upstairs room, disheartened (7)
I believe the answer is:
fanatic
'zealot's' is the definition.
(thesaurus)
'cooler upstairs room disheartened' is the wordplay.
'cooler' becomes 'fan' (I've seen this before).
'upstairs room' becomes 'attic' (I've seen this before).
'disheartened' says to hollow out the word (remove centre letters).
'attic' with its centre taken out is 'atic'.
'fan'+'atic'='FANATIC'
'found in' is the link.
(Other definitions for fanatic that I've seen before include "enthusiastic" , "One who is excessively zealous" , "crank" , "Bigot - enthusiast" , "Person filled with excessive zeal for cause" .)