Within the first day of running the unit, you should look around the furnace to make sure there is no water running down the side, onto the floor. If there is water, the drain might be plugged. This will need to be cleaned out by blowing air into it. If there is a plug, the water running down into the furnace will ruin the controls.
Make sure to check the outside unit and remove the cover, or anything that is on the top or sides, of the unit. If the Air Conditioning unit runs with the cover on, your going to need a new motor in just one day! It may kill the compressor of the unit, or start a fire!
Go to your Furnace and replace the filter. If the filter is dirty it will make your blower draw more amps and cost more to run. If the filter is dirty it can cause icing on the coil above the furnace and not cool your home. Note: (Buy the cheaper filters, because they will pull out junk in the air. If you get the $5 "better" filters, they will catch alot more dust, much faster. These will need to be changed, or at least looked at, once a month.) I personally use the cheap filters. You should aso get an air cleaner if you have trouble with allergies. The Blue-Tube MaxLife UV germicidal ultraviolet light system, enhanced with OST™ Odor Sanitizing Technology. OST™ uses multiple wavelengths of light to significantly reduce odors. We have installed this unit for customers that have allergies and they can advise on how well this works.