Sounds like an oxymoron, doesn’t it? Well, believe it or not, if you have central air conditioning, elements in the furnace can freeze up. If you have dirty coils and a very humid day, the moist air won’t be able to pass through the coils fast enough to allow them to “warm up”. So they freeze. Usually this can be fixed by cleaning the coils. It’s also important to check the refrigerant level in the unit. If it is low, it can also contribute the frost over.