Although I haven’t been there in a while, I don’t think they actually MU. They couple iron and air only and one tows the other in the appropriate direction. One of the members told me they used to do that with the Hi-V/Lo-V also.
I stand corrected,,thank you sir. I believe the only train line air is brake pipe so each compressor will operate separately and charge it's own MR pipe since there is no electric synchronizing switch.
There was a G/O taking out Track B4 from 42 Street - Bryant Park to 59 Street - Columbus Circle, was there not? Northbound (D) trains were operating via Eighth Avenue, and thus, so was the holiday train.