There is one difference between Sleeper & AC-3 Tier (Not AC Economy) Coaches and that's the make up of coach windows. Sleeper Coach has Rounded Square windows with 4 horizontal iron bars where as AC-3 Tier Coach usually has Rounded Rectangle Windows replaced by Double(Single in LHB) Glasses instead of the iron bars.
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ICF AC Coaches (2nd or 3rd AC) have Four Horizontal Iron Bars on the coach main gate window & toilet window but not in the case of RCF Non-LHB AC Coaches. Sleeper Coaches (Non-LHB of both ICF & RCF)...
more... have around 10 Horizontal Iron Bars on coach main gate windows.