Switch on air-conditioning, worried about temperature you said? (7)
I believe the answer is:
actuate
'switch on' is the definition.
(I've seen this before)
'air-conditioning worried about temperature you said?' is the wordplay.
'air conditioning' becomes 'AC'.
'worried' becomes 'ate' (something worrying may eat someone up).
'about' is a charade indicator (letters next to each other).
'temperature' becomes 't' (abbreviation).
'you said?' becomes 'U' (homophone of 'you').
't'+'u'='tu'
'ate' put after 'tu' is 'tuate'.
'ac'+'tuate'='ACTUATE'
(Other definitions for actuate that I've seen before include "Put into effect" , "Trigger off, energise" , "Inspire" , "Switch on" , "Cause to operate" .)