The most common and most likely answer to this crossword clue is the 13 letter word REFRIGERATION
I've seen this crossword clue in The Times
R
E
F
R
I
G
E
R
A
T
I
O
N
More clues leading to the result REFRIGERATION
Buddy explains!
The straight part
We know that "Cooling down" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cooling down = refrigeration.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does REFRIGERATION mean?
REFRIGERATION noun- The process of transferring heat from an object in order to cool it.
- The process of preserving something by cooling.
- The cooling of the body for therapeutic purposes.