Is the plant 'well established' or still 'growing in'? Perhaps needs a little more water, especially if the heater from the air con is 'sucking the moisture' out of the soil?

It is still growing in, very little root system established as yet!

Hi, Most plants (indoor or out) will 'shut down' if they're in a constantly windy spot - they literally close their stomata to stop all the water evaporating from their leaves. They can also become dehydrated very quickly just from the warm air causing water to evaporate from the soil. So relocating your philodendron should be priority number one. Once you've done that I'd recommend some gentle TLC: put your finger into the potting mix to see if its dry under the surface, and if so give your plant a thorough water, making sure the pot drains well (you don't want the plant sitting in water, which will rot any new roots). Then find a warm (but not drafty) spot with the best light you can. You may also want to try a little bit of liquid fertilizer - I'd apply this at half the recommended strength as you just want your plant to recover at this stage rather than put out lots of new growth. If the cutting is still rooting, you could also prune it as it looks like there's quite a bit of plant above the soil compared to what's going on under the soil. Good luck!