I’m including @Countryboyjvd1971 as I know your very knowledgeable when it comes to HVAC.
I cool my grow room primarily with a window A/C unit. It worked fine for the summer and I’m wondering what to expect this fall as the temperatures outside drop. Will it continue to perform?
Part of me says “yes” b/c it should be easier to dump the heat to the outside. But, I don’t know any of the details. What about when it’s <32F outside?
If it is a window unit and your area gets cold winters, I would be worried about too much cold air getting in. Even when off air can get through the window unit right?
When the real winter sets in I’ll have to reasses my situation. It would be nice if the window A/C unit would act as a thermostat and continue to keep the room temperature at 70 
Is window unit a digital control or old scool type ?
If digital it will still run as long as long as there’s a call for cooling the old school type tstats in window Ac are effected by outdoor temps
With that said Ac system weather a window unit or central air unit will have a tendency to freeze up when outdoor temperatures drop below 45 degrees
Due to saturation temp of refrigerant
Most Ac systems that will run in winter have fan cycle controls to keep outdoor fan from running until head pressure is high enough alowing for proper subcooling of refrigerant
Un fortunately widow unit can not be set up this way
Suggestion if you have low temps like that and need to cool room bringing in some fresh air from out side would cool room and save you $ on cooling cost
When temps are below say 50 you would have free cooling if you have a fresh air fan installed then you’d have options 
Any way that’s how I would set it up myself @HappyCamper
I completely agree @Countryboyjvd1971 I would like to add that running a window unit in the winter, in a room with high humidity, you run the risk of it freezing up and if that were to happen and you don’t notice, the room temp will rise. i say open your fresh air and take advantage of the cool air from out side.
@Countryboyjvd1971, @greenthumbfun - Wow, I wouldn’t have guessed that I’d have issues at around 50F. Our nighttime lows are in the low 50s now! I guess each night I’ll switch the unit to “Fan” and back to cool during the day.
Once daytime winter temps are here, I’ll switch to a window fan. Do they make them with built-in thermostats? Or, do I need a separate one that the fan will plug into?
i did a google search and it looks like they do make window fans with a thermostat. but if your in 50s at night all ready then i would be cautious with your temps. cold and herb plants do not mix
Yes @Countryboyjvd1971, it’s a digital unit.
I see one that, in addition to having a thermostat, it ‘exchanges’ the air in the room. Dual fans, one blowing in and the other blowing out.
Then is should run as explained up above
You may have issue when outdoor temp drop
I stand by my suggestion of free cooling @HappyCamper
Invest in a inexpensive inline fan to bring some cold air in from outside in cold weather