Nope, this is not neccessarily true. Generallt the prices are lowest during march. Also, if you pre-buy now , you loose on the warranty period (ofc you won't use it unless u buy a hot/cold one) and also the unit will be untested for any manufacturing defects plus will take up ur space too, and all this isn't worth it even if you save a few bucks.
My advice would be to buy things at the time when you require them, especially when it is electronics.
If you still opt for an ac, do make sure if you are getting the extended warranty (1+4) offers and free installation offers now or not, because during spring/summer season all brands nowadays provides these offers.