Section 17(2) in The Railway Passengers (Cancellation of Ticket and Refund of Fare) Rules, 2015
(2)The refund of difference of fare under sub-rule (1) shall be granted at the destination station on production of the ticket along with a certificate from the ticket checking staff of the train giving particulars of the ticket, number of the coach and stations between which the air-conditioning facility was not provided, and is presented within twenty hours of arrival of the train.
