Would anyone know if the 133.375 frequency cover's the 119.325 sector as well during slow times of traffic at FL'S 310-350 ?
In the past I've heard them merge these two sectors together when traffic is slow, they always seem to use 133.375 as the primary. When it gets really slow, like at night, they use 133.375 for all the Area 4 sectors.
Secondly is it split between 119.325/133.375 under 120.325 when traffic doe's pick up ?
Yes, this seems to be the normal configuration, from what I've heard anyway.
I heard this morning SW Fligt 816 handed off from 120.325 to 133.375 when it would have been 119.325 at the flight level it was traveling at.
SWA816 = PVD-MDW. From what I can tell Cleveland appears to have an LOU with Chicago to feed them MDW arrivals inbound via J60.GSH at FL300 maximum (60 miles east of GSH at FL300 seems to be the common restriction). So presumably you heard 816 get the handoff from 120.325 to 119.325(split)/133.375(merged) while in the descent to FL360 or level at FL360. Traffic in cruise at FL360 westbound via J60 would get the handoff from Cleveland on 120.325 over to Chicago on 124.825.