Fan and ventilator to tackle damp, occasionally (7)
I believe the answer is:
admirer
'fan' is the definition.
(an admirer is a fan of something)
'ventilator to tackle damp occasionally' is the wordplay.
'ventilator' becomes 'airer' (I've seen this in another clue).
'to tackle' is an insertion indicator (tackle can mean to take hold of).
'occasionally' indicates alternate letters (letters taken at regular intervals or occasions).
The alternating letters of 'damp' are 'dm'.
'airer' placed around 'dm' is 'ADMIRER'.
'and' acts as a link.
(Other definitions for admirer that I've seen before include "Married to one who thinks highly of" , "Romantic adorer" , "girlfriend?" , "potential suitor" , "Married (anag) -- lover" .)