Not working is unacceptable (3,2,5)
I believe the answer is:
out of order
I believe this is a double definition.
'not working' is the first definition.
(I've seen this before)
'unacceptable' is the second definition.
(I've seen this before)
'is' is the link.
(Other definitions for out of order that I've seen before include "unusually arranged" , "having left monastery?" , "(Mechanism) broken" , "Ex-nun is" , "Disgraced knight might be told to get this" .)