I think you need to add a little more info. such as temps in winter where the orchids are. Under lights? Are they near a window? What sort of mix are they in? etc. No drainage holes makes your task difficult, but it is probably too late in the the growing season to repot.

I usually keep the house at 19 or 20C. I have one right by a south window with a bamboo shade that can be up or down during the day, one is a metre from a frosted west window in a bathroom and one is in a room about 2 metres from an east picture window and 2 metres from a south window. I can move them about anywhere, even a north window if necessary. They are in what seems to be only bark with no soil at all. They were likely purchased from a WalMart or big box, probably not a specialty place of any kind.

Apart from no drainage holes it all sounds good. Mine spend the year indoors and in the cooler months they get sunlight filtered through a matchstick blind because the sun has moved north in the sky (Southern Hemisphere).

Watering interval in winter is about once a week in a mostly treated pine bark mixture.

Sorry, not much help, I have about 1000 orchids in pots with drainage holes or on mounts. So growing something in a pot without a drainage hole is a mystery.

Thank you Arthurm, I also wonder why orchids are sold en masse in these pots with no drainage, but I will do my best to see them through this winter by keeping a careful eye on the water sitting in the bottom. They are so beautiful I may be encouraged to carry on with some of my own, I'll start with a couple and you'll be hearing from me if I work my way towards a 1000!!

Thank you dannie, that's what I will do, fill them up and drain them.