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' means one lot of letters go next to another.
'temperature' becomes 't' (abbreviation).
'you said?' becomes 'U' (homophone of 'you').
't'+'u'='tu'
'ate' 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" .)