When it's time to switch your HVAC system from your air conditioner to your heater, there are certain steps that you should take. Taking these steps will ensure that your system is kept in great condition no matter what happens throughout the winter. First, you can start by preparing your air conditioner using these steps:

Remove Window Units

If you have any window units, you should take them out and store them in your home. Some people believe that they can leave these units in their windows throughout the winter; however, you can preserve them better by taking them out until you're ready to use them the following summer.

Clean the Unit

If you have a unit outside of your home, you should take the time to clean it. Remove any debris that has been trapped inside of your unit, such as leaves, twigs, and branches. Then, clean the unit by using a hose to spray away dirt and dust. Be careful not to bend the fans or damage any of the parts. Allow your unit to dry completely before moving to the next step.

Get a Cover

Place a cover over your unit. This will prevent any debris from getting into it over the winter. You can purchase a cover at a home improvement store. If you don't have a plastic cover and don't want to go purchase one, you can use a tarp and rocks to cover the unit and prevent moisture and other debris from getting to the unit.

Change the Air Filter

Inside of your home, you should locate the air filter. If you haven't already changed the air filter, take the time to do so. Your air filter should be replaced every 3-4 months. If you live in an area near construction or that gets a lot of wind, you may find that it's necessary to change the filter more often. Changing the filter will prevent it from becoming clogged, which can force your HVAC system to work harder to push the air throughout your home.

After winterizing your HVAC system, you can prepare your heater for the coming months. Have a professional come to your home to tune up the system. This will include making sure that everything is in working order and that there are no repairs that are needed to make sure that it will run throughout the winter. If there are any problems, you can have it repaired before the problem becomes much larger, leaving you cold in the middle of the winter.

Source Credit: http://www.airmasterheatingandair.com/How%20to%20Winterize%20Your%20HVAC%20System.html