I have a 8810A and just tried that and it seemed to be no different to just the AUTO position. Of course its not meant to be used like that and the reading is just drift, (input charging), with no connection to the inputs due to being on the 200mV range and high I/P Z.
One important thing to check is if the unit has both AC V and OHMS options installed (Yes they were options on the 8810A).
Just had a look at the photos and the options section on the photo of the bottom do not have a mark in the square indicating installed.
When the options were not installed there was also a special metal strip that was inserted in the DC AC and OHMS switch bank to prevent the AC and OHMS functions from being selected.
One interesting thing is the model 8800A AC V and OHMS modules which came installed in that model (not as options IIRC) will transplant into the 8810A but the OHMS module has an on board battery for the ohms supply !!!! which means the covers have to come off to replace it. Silly idea on a bench meter.
But in the 8810A they got rid of the battery and used an isolated supply as it should be.
I would avoid those without the options unless really cheap , maybe its time for an offer.