Clue: Freak ringing Mercury up in capital (Asian capital) (7)
Answer: AFGHANI
Explanation: Definition: Asian capital
A double envelope ('ringing' and 'in') of GH, a reversal ('up' in a down light) of HG (chemical symbol, 'mercury') in FAN ('freak'), all in AI (A- one, 'capital'). The AFGHANI is the unit of currency in (where else?) Afghanistan.