See if you can spot any ice on the lines on the inside and outside unit. Chances are the coils are frozen. You will need to let it defrost if this is the case. Could take up to 24 hours. Or less than an hour of you run the heat. Be prepared for water to leak from the inside unit as the drain may not keep up. Once fully thawed (you'll never know when unless you can see inside an access panel, so longer is better) you can run it again. You should change the filter as low air flow can lead to frozen coils. If it happens again with a fresh filter, chances are it has low refrigerant and needs to be charged by an HVAC tech. If it's low after one year, you probably have a leak somewhere. Hopefully it's under warranty still.