A week after Sydney's biggest public transport timetable overhaul, rail passengers are taking more journeys than they would like on older "S-set" trains without air conditioning.

Dating to the 1970s, S-sets have been put to use in greater numbers on several lines to accommodate an extra 1500 weekly services introduced as part of the timetable changes.

A leaked Sydney Trains document shows an increase in the use of S-set trains during peak periods on the South and Inner West, Bankstown and Airport and East Hills lines.

The Inner West and South lines have the most during peak periods of the day with eight S-sets operating in the morning and six in the evening.