New items like appliances, heaters and air conditioners generally don’t increase the value of a property when you are selling it because other homes also have these items as well. New amenities can help a house to sell faster because buyers know they won’t need to be replaced in the near future.
Many home sellers make the mistake of increasing the price of their property by the amount of the improvement which then makes it overpriced. That can obviously hurt the sale.
If appliances and other components are working just purchase a one-year home warranty for the buyer in case they stop functioning. Only replace items that are broken since buyers tend to reduce the value of the item by much more than its replacement cost. This is because they will want you to buy them a top-of-the line model not just a basic one.