Problem with air-conditioning plant (5)
I believe the answer is:
sumac
'plant' is the definition.
The answer is an example.
'problem with air-conditioning' is the wordplay.
'problem' becomes 'sum' (as in a mathematical problem).
'with' says to put letters next to each other.
'air conditioning' becomes 'AC'.
'sum'+'ac'='SUMAC'
(Other definitions for sumac that I've seen before include "purchase from garden centre?" , "Shrub or small tree - Camus (anag)" , "Shrub colourful in Autumn" , "Smoke-bush" , "Small tree bright in autumn" .)